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  • Springer  (1,386)
  • Chemistry and Pharmacology  (1,386)
  • 1
    Electronic Resource
    Electronic Resource
    Activity and stability of Cu/ZnO/Al2O3 catalyst promoted with B2O3 for methanol synthesis (2000)
    Springer
    Catalysis letters 68 (2000), S. 55-58 
    Details
    ISSN: 1572-879X
    Keywords: promoting effect ; B2O3 ; Cu/ZnO/Al2O3 catalyst ; methanol synthesis ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The addition of B2O3 to a Cu/ZnO/Al2O3 catalyst increased the activity of the catalyst for methanol synthesis after an induction period during the reaction. The stability of the B2O3-containing Cu/ZnO/Al2O3 catalyst was greatly improved by the addition of a small amount of colloidal silica to the catalyst.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019010831562
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  • 2
    Electronic Resource
    Electronic Resource
    Stability and excitation of potassium promoter in iron catalysts – the role of KFeO2 and KAlO2 phases (2000)
    Springer
    Catalysis letters 67 (2000), S. 129-134 
    Details
    ISSN: 1572-879X
    Keywords: potassium desorption ; stability ; excitation ; iron catalyst ; Rydberg atoms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Well‐characterized catalyst model compounds of KAlO2 and KFeO2 are investigated by thermal desorption of potassium from the material. The desorbing fluxes of ions, atoms and highly excited states (field ionizable Rydberg states) were studied with surface and field ionization detectors in a vacuum apparatus. From the Arrhenius plots the activation energies for desorption of K and K+ were determined. The chemical state of potassium at the surfaces is concluded to be: ionic on KAlO2 (with the K desorption barrier of 1.76 eV) and covalent on KFeO2 (barrier of 2.73 eV). These results agree with the data obtained earlier for industrial catalysts for ammonia and styrene production. They are interpreted in terms of the Schottky cycle, which is completed for KAlO2 and fails for KFeO2. This failure indicates a non‐equilibrium desorption process. K Rydberg states are only found to desorb from KFeO2, in agreement with the suggestion that such states in some way are responsible for the catalytic activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019013504729
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  • 3
    Electronic Resource
    Electronic Resource
    Defect structure of the low temperature α-cristobalite phase and the cristobalite ⇆ tridymite transformation in (Si-Ge)O2 (2000)
    Springer
    Physics and chemistry of minerals 27 (2000), S. 386-397 
    Details
    ISSN: 1432-2021
    Keywords: Key words Cristobalite ; Tridymite ; Phase transformation ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Using minimum exposure techniques, it is feasible to perform high resolution electron microscopy on the α-cristobalite phase of (Si0.9 Ge0.1)O2, which is extremely radiation sensitive. Such images reveal atomic scale information of twins and tridymite-like stacking faults on (1 1 1)β planes, as well as of domain boundaries resulting from the β→α transition. Polytype structures are formed in certain cases. Morphological features suggest that the phase transformation cristobalite → tridymite proceeds by means of a zonal dislocation mediated synchro-shear process on (1 1 1)β planes; the geometry of this process is analyzed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002699900082
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of Ca2+ on the Activity and Stability of Methanol Dehydrogenase (2000)
    Springer
    The protein journal 19 (2000), S. 469-473 
    Details
    ISSN: 1573-4943
    Keywords: Methanol dehydrogenase ; Ca2+ ; binding ; activity ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effects of exogenously added Ca2+ on the enzymatic activity and structural stability of methanol dehydrogenase were studied for various Ca2+ concentrations. Methanol dehydrogenase activity increased significantly with increasing concentration of Ca2+, approaching saturation at 200 mM Ca2+. The effect of Ca2+ on the activation of MDH was time dependent and Ca2+ specific and was due to binding of the metal ions to the enzyme. Addition of increasing concentration of Ca2+ caused a decrease of the intrinsic tryptophan fluorescence intensity in a concentration-dependent manner to a minimum at 200 mM, but with no change in the fluorescence emission maximum wavelength or the CD spectra. The results revealed that the activation of methanol dehydrogenase by Ca2+ occurred concurrently with the conformational change. In addition, exogenously bound Ca2+ destabilized MDH. The potential biological significance of these results is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026597314542
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  • 5
    Electronic Resource
    Electronic Resource
    Evidence for stable grain boundary melt films in experimentally deformed olivine-orthopyroxene rocks (2000)
    Springer
    Physics and chemistry of minerals 27 (2000), S. 480-494 
    Details
    ISSN: 1432-2021
    Keywords: Key words Olivine ; Grain boundary ; Partial melt ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The microstructure of olivine-olivine grain boundaries has been studied in experimentally deformed (1200–1227 °C, 300 MPa) partially molten olivine and olivine-orthopyroxene rocks. In-situ melting produced ∼1 vol% melt in all samples studied. Grain boundary analyses were carried out using a number of transmission electron microscopy techniques. The grain boundary chemistry in undeformed olivine-orthopyroxene starting material showed evidence for the presence of an intergranular phase along some, but not all, of the olivine-olivine boundaries. In the deformed samples, ultrathin Si-rich, Al- and Ca-bearing amorphous films have been observed along all investigated olivine-olivine grain boundaries. The chemistry of the grain boundaries, which is considered to be indicative for the presence of a thin film, was measured with energy-dispersive X-ray spectroscopy (EDX) and energy-filtering imaging. The amorphous nature of the films was confirmed with diffuse dark field imaging, Fresnel fringe imaging, and high-resolution electron microscopy. The films range in thickness from 0.6 to 3.0 nm, and EDX analyses show that the presence of Al and Ca is restricted to this ultrathin film along the grain boundaries. Because thin melt films have been observed in all the samples, they are thought to be stable features of the melt microstructure in deformed partially molten rocks. The transition from the occasional presence of films in the undeformed starting material to the general occurrence of the films in deformed materials suggests that deformation promotes the formation and distribution of the films. Alternatively, hot-pressing may be too short for films to develop along all grain boundaries. A difference in creep strength between the studied samples could not be attributed to grain boundary melt films, as these have been found in all deformed samples. However, a weakening effect of grain boundary melt films on olivine rheology could not be ruled out due to the lack of confirmed melt-film free experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690000090
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  • 6
    Electronic Resource
    Electronic Resource
    Numerical solutions for a coupled non-linear oscillator (2000)
    Springer
    Journal of mathematical chemistry 28 (2000), S. 325-340 
    Details
    ISSN: 1572-8897
    Keywords: numerical method ; stability ; Hopf bifurcation ; coupled oscillator
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mathematics
    Notes: Abstract A second-order accurate numerical method has been proposed for the solution of a coupled non-linear oscillator featuring in chemical kinetics. Although implicit by construction, the method enables the solution of the model initial-value problem (IVP) to be computed explicitly. The second-order method is constructed by taking a linear combination of first-order methods. The stability analysis of the system suggests the existence of a Hopf bifurcation, which is confirmed by the numerical method. Both the critical point of the continuous system and the fixed point of the numerical method will be seen to have the same stability properties. The second-order method is more competitive in terms of numerical stability than some well-known standard methods (such as the Runge–Kutta methods of order two and four).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011025104111
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  • 7
    Electronic Resource
    Electronic Resource
    1,3-Dihydrobenzo[c]thienylium (thiophthalylium) salts. (Review) (2000)
    Springer
    Chemistry of heterocyclic compounds 36 (2000), S. 115-133 
    Details
    ISSN: 1573-8353
    Keywords: thiophthalylium salts ; methods of preparation ; structure ; stability ; reactivity ; electrophilic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Methods of preparation, chemical reactions, the structures and reactivity of thiophthalylium ions are reviewed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02283539
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  • 8
    Electronic Resource
    Electronic Resource
    The Equation of State of Lakes (2000)
    Springer
    Aquatic geochemistry 6 (2000), S. 1-17 
    Details
    ISSN: 1573-1421
    Keywords: lakes ; density ; compressibility ; expansibility ; conductivity ; stability ; pvt properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract In recent years, a number of workers have studied the stability of deep lakes such as Lake Tanganyika, Lake Baikal and Lake Malawi. In this paper, the methods that can be used to determine the effect that the components of lakes have on the equation of state are examined. The PVT properties of Lakes have been determined by using apparent molal volume data for the major ionic components of the lake. The estimated PVT properties (densities, expansibility and compressibilities) of the lakes are found to be in good agreement with the PVT properties (P) of seawater diluted to the same salinity. This is similar to earlier work that showed that the PVT properties of rivers and estuarine waters could also be estimated from the properties of seawater. The measured densities of Lake Tanganyika were found to be in good agreement (± 2 × 10-6 g cm-3) with the values estimated from partial molal properties and the values of seawater at the same total salinity (ST = 0.568‰). The increase in the densities of Lake Tanganyika waters increased due to changes in the composition of the waters. The measured increase in the measured density (45 × 10-6 g cm-3) is in good agreement (46 × 10-6 g cm-3) with the values calculated for the increase in Na+, HCO3 -, Mg2+, Ca2+ and Si(OH)4. Methods are described that can be used to determine the conductivity salinity of lakes using the equations developed for seawater. By combining these relationships with apparent molal volume data, one can relate the PVT properties of the lake to those of seawater.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009626325650
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  • 9
    Electronic Resource
    Electronic Resource
    Highly Active and Stable Pt-USY in the Low-Temperature de-NOx HC-SCR (2000)
    Springer
    Reaction kinetics and catalysis letters 71 (2000), S. 33-40 
    Details
    ISSN: 1588-2837
    Keywords: Pt-USY ; de-NOx ; HC-SCR ; propene ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Selective catalytic reduction of NOx by propene has been investigated on Pt-USY and compared to other Pt-catalysts. The catalyst was characterized by XRD, Ar adsorption at 87 K, TEM, and CO chemisorption, and tested in a gas mixture system in excess oxygen. Pt-USY shows an excellent activity in the reaction, with a molar NOx conversion of 90% at 475 K. Stability during time-on-stream and resistance to SO2 and H2O in the feed stream has also been investigated. Pt-USY performs better under lean-burn conditions than other Pt-catalysts on ZSM-5, Al2O3, or SiO2. The selectivity to N2 was similar for all the catalysts (∼30%), the other major product being N2O.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1010365628369
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  • 10
    Electronic Resource
    Electronic Resource
    Formulation Development and Antitumor Activity of a Filter-Sterilizable Emulsion of Paclitaxel (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 175-182 
    Details
    ISSN: 1573-904X
    Keywords: paclitaxel ; emulsions ; filter-sterization ; particle size ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Paclitaxel is currently administered i.v. as a slow infusion of asolution of the drug in an ethanol:surfactant:saline admixture. However,poor solubilization and toxicity are associated with this drug therapy.Alternative drug delivery systems, including parenteral emulsions, areunder development in recent years to reduce drug toxicity, improveefficacy and eliminate premedication. Methods. Paclitaxel emulsions were prepared by high-shearhomogenization. The particle size of the emulsions was measured by dynamiclight scattering. Drug concentration was quantified by HPLC and invitro drug release was monitored by membrane dialysis. The physicalstability of emulsions was monitored by particle size changes in boththe mean droplet diameter and 99% cumulative distribution. Paclitaxelpotency and changes in the concentration of known degradants wereused as chemical stability indicators. Single dose acute toxicity studieswere conducted in healthy mice and efficacy studies in B16 melanomatumor-bearing mice. Results. QW8184, a physically and chemically stable sub-micronoil-in-water (o/w) emulsion of paclitaxel, can be prepared at high drugloading (8-10 mg/mL) having a mean droplet diameter of 〈100 nmand 99% cumulative particle size distribution of 〈200 nm. In vitro release studies demonstrated low and sustained drug release both inthe presence and absence of human serum albumin. Based on singledose acute toxicity studies, QW8184 is well tolerated both in miceand rats with about a 3-fold increase in the maximum-tolerated-dose(MTD) over the current marketed drug formulation. Using the B16mouse melanoma model, a significant improvement in drug efficacywas observed with QW8184 over Taxol®. Conclusions. QW8184, a stable sub-micron o/w emulsion of paclitaxelhas been developed that can be filter-sterilized and administered i.v.as a bolus dose. When compared to Taxol®, this emulsion exhibitedreduced toxicity and improved efficacy most likely due to thecomposition and dependent physicochemical characteristics of the emulsion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007565230130
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  • 11
    Electronic Resource
    Electronic Resource
    Protein Spray-Freeze Drying. Effect of Atomization Conditions on Particle Size and Stability (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 1374-1382 
    Details
    ISSN: 1573-904X
    Keywords: particle size ; PLG microspheres ; protein delivery ; spray-freeze drying ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To investigate the effect of atomization conditions on particle size and stability of spray-freeze dried protein. Methods. Atomization variables were explored for excipient-free (no zinc added) and zinc-complexed bovine serum albumin (BSA). Particle size was measured by laser diffraction light scattering following sonication in organic solvent containing poly(lactide-co-glycolide) (PLG). Powder surface area was determined from the N2 vapor sorption isotherm. Size-exclusion chromatography (SEC) was used to assess decrease in percent protein monomer. Fourier-transform infrared (FTIR) spectroscopy was employed to estimate protein secondary structure. PLG microspheres were made using a non-aqueous, cryogenic process and release of spray-freeze dried BSA was assessed in vitro. Results. The most significant atomization parameter affecting particle size was the mass flow ratio (mass of atomization N2 relative to that for liquid feed). Particle size was inversely related to specific surface area and the amount of protein aggregates formed. Zinc-complexation reduced the specific surface area and stabilized the protein against aggregation. FTIR data indicated perturbations in secondary structure upon spray-freeze drying for both excipient-free and zinc-complexed protein. Conclusions. Upon sonication, spray-freeze dried protein powders exhibited friability, or susceptibility towards disintegration. For excipient-free protein, conditions where the mass flow ratio was 〉 ∼0.3 yielded sub-micron powders with relatively large specific surface areas. Reduced particle size was also linked to a decrease in the percentage of protein monomer upon drying. This effect was ameliorated by zinc-complexation, via a mechanism involving reduction in specific surface area of the powder rather than stabilization of secondary structure. Reduction of protein particle size was beneficial in reducing the initial release (burst) of the protein encapsulated in PLG microspheres.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007570030368
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  • 12
    Electronic Resource
    Electronic Resource
    Thermal Analysis, Microcalorimetry and Combined Techniques for the Study of Pharmaceuticals (1999)
    Springer
    Journal of thermal analysis and calorimetry 56 (1999), S. 1285-1304 
    Details
    ISSN: 1572-8943
    Keywords: amorphous state ; combined techniques ; drug design ; drug product development ; drug substance ; drug technology ; DSC ; excipients ; failure investigations ; hydrates ; MDSC ; microcalorimetry ; pharmaceuticals ; polymorphism ; polymers ; preformulation ; process optimization ; purity ; quality control ; solvates ; stability ; sub-ambient DSC ; TG ; temperature resolved X-ray diffraction ; water interactions ; thermal microscopy ; water sorption-desorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Modern thermal analysis, microcalorimetry and new emerging combined techniques which deliver calorimetric, microscopic and spectroscopic data offer a powerful analytical battery for the study of pharmaceuticals. These techniques are very useful in all steps of development of new drug products as well as methods for quality control in production. The characterization of raw materials enables to understand the relationships between polymorphs, solvates and hydrates and to choose the proper development of new drug products with very small amount of material in a very short time. Information on stability, purity is valuable for new entities as well as for marketed drug substances from different suppliers. Excipients which vary from single organic or inorganic entity to complexes matrixes or polymers need to be characterized and properly controlled. The thermodynamic phase-diagrams are the basis of the studies of drug-excipients interactions. They are very useful for the development of new delivery systems. A great number of new formulations need proper knowledge of the behaviour of the glass transition temperature of the components. Semi-liquid systems, interactions in aqueous media are also successfully studied by these techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1010194020563
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  • 13
    Electronic Resource
    Electronic Resource
    Ignitability of Polymers Related to Polymer Properties and Different Steady States of Combustion Theoretical Approach (1999)
    Springer
    Journal of thermal analysis and calorimetry 55 (1999), S. 727-739 
    Details
    ISSN: 1572-8943
    Keywords: ignition ; polymer combustion modelling ; stability ; steady state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A mathematical model of ignition and burning of organic polymers was used for evaluation and quantification of the tendency of polymers to ignition. The model permits investigation of the influence of one parameter of the polymer on the others. It was found that the model could be used for the verification of the ignitability method developed by Miller et al. [1]. Different steady states of combustion were found when using the model proposed. There is a characteristic steady state for normal flaming combustion, another for non-flaming combustion, and there are also unstable steady states that have no real physical meaning.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1010157011275
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  • 14
    Electronic Resource
    Electronic Resource
    Thermodynamics of a 24-Mer Triple Helix Formation and Stability (1999)
    Springer
    Journal of thermal analysis and calorimetry 56 (1999), S. 1177-1184 
    Details
    ISSN: 1572-8943
    Keywords: differential scanning calorimetry ; DNA triple helix ; oligonucleotides ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In this work we report a thermodynamic characterization of stability and melting behaviour of two 24-mer DNA triplexes. The third strand, that binds the Watson-Crick double helix with Hoogsteen hydrogen bonds, contains 3′-3′ phosphodiester junction that determines the polarity inversion. The target double helix is composed of adjacent and alternate fragments of oligopurine-oligopyrimidine tracts. The two helices differ from the substitution of the cytosine, involved in the junction, with the thymine. Calorimetric data reported here provide a quantitative measure of the influence of pH and base modification on the stability of a DNA triplex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1010117431041
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  • 15
    Electronic Resource
    Electronic Resource
    Bicelle-based liquid crystals for NMR-measurement of dipolar couplings at acidic and basic pH values (1999)
    Springer
    Journal of biomolecular NMR 13 (1999), S. 187-191 
    Details
    ISSN: 1573-5001
    Keywords: alignment ; bicelle ; dipolar coupling ; liquid crystal ; pH ; stability ; ubiquitin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract It is demonstrated that mixtures of ditetradecyl- phosphatidylcholine or didodecyl-phoshatidylcholine and dihexyl- phosphatidylcholine in water form lyotropic liquid crystalline phases under similar conditions as previously reported for bicelles consisting of dimyristoyl-phosphatidylcholine (DMPC) and dihexanoyl- phosphatidylcholine (DHPC). The carboxy-ester bonds present in DMPC and DHPC are replaced by ether linkages in their alkyl analogs, which prevents acid- or base-catalyzed hydrolysis of these compounds. 15N-1H dipolar couplings measured for ubiquitin over the 2.3–10.4pH range indicate that this protein retains a backbone conformation which is very similar to its structure at pH 6.5 over this entire range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008395916985
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  • 16
    Electronic Resource
    Electronic Resource
    Preparation and Characterization of Carmustine Loaded Polyanhydride Wafers for Treating Brain Tumors (1999)
    Springer
    Pharmaceutical research 16 (1999), S. 762-765 
    Details
    ISSN: 1573-904X
    Keywords: polymer implant ; brain cancer ; carmustine ; polyanhydride ; stability ; controlled release
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011995728760
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  • 17
    Electronic Resource
    Electronic Resource
    Formulation and Lyoprotection of Poly(Lactic Acid-Co-Ethylene Oxide) Nanoparticles: Influence on Physical Stability and In Vitro Cell Uptake (1999)
    Springer
    Pharmaceutical research 16 (1999), S. 859-866 
    Details
    ISSN: 1573-904X
    Keywords: nanoparticles ; poly(lactic acid) ; poly(lactic acid-co-ethylene oxide) ; freeze-drying ; stability ; flow cytometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To investigate the feasibility of producing freeze-dried poly-(ethylene oxide) (PEO)-surface modified nanoparticles and to study their ability to avoid the mononuclear phagocytic system (MPS), as a function of the PEO chain length and surface density. Methods. The nanoparticles were produced by the salting-out method using blends of poly(D,L-lactic acid) (PLA) and poly(D,L-lactic acid-co-ethylene oxide) (PLA-PEO) copolymers. The nanoparticles were purified by cross-flow filtration and freeze-dried as such or with variable amounts of trehalose as a lyoprotectant. The redispersibility of the particles was determined immediately after freeze-drying and after 12 months of storage at −25° C. The uptake of the nanoparticles by human monocytes was studied in vitro by flow cytometry. Results. PLA-PEO nanoparticles could be produced from all the polymeric blends used. Particle aggregation after freeze-drying was shown to be directly related to the presence of PEO. Whereas this problem could be circumvented by use of trehalose, subsequent aggregation was shown to occur during storage. These phenomena were possibly related to the specific thermal behaviours of PEO and trehalose. In cell studies, a clear relationship between the PEO content and the decrease of uptake was demonstrated. Conclusions. The rational design of freeze-dried PEO-surface modified nanoparticles with potential MPS avoidance ability is feasible by using the polymer blends approach combined with appropriate lyoprotection and optimal storage conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018826103261
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  • 18
    Electronic Resource
    Electronic Resource
    Isolation, Characterization, and Stability of Positional Isomers of Mono-PEGylated Salmon Calcitonins (1999)
    Springer
    Pharmaceutical research 16 (1999), S. 813-818 
    Details
    ISSN: 1573-904X
    Keywords: calcitonin ; polyethylene glycol ; PEGylation ; peptide ; tryptic digestion ; stability ; HPLC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To separate and characterize the different positional isomers of mono-PEGylated salmon calcitonins (mono-PEG-sCTs) and to evaluate the effects of the PEGylation site on the stability of different mono-PEG-sCTs in rat kidney homogenate. Methods. Mono-PEG-sCTs were prepared using succinimidyl carbonate monomethoxy polyethylene glycol (5,000 Da) and separated by gel-filtration HPLC followed by reversed-phase HPLC. To characterize PEGylated sCTs, matrix-assisted laser desorption ionization time of flight mass spectrometry (M ALDI-TOF MS) and reversed-phase HPLC of the trypsin digested samples were performed. Mono-PEG-sCTs and sCT in rat kidney homogenates were measured by column-switching reversed-phase HPLC with on-line detection of the radioiodinated samples using a flow-through radioisotope detector. Results. Three different mono-PEGylated sCTs were separated by reversed-phase gradient HPLC. From the MALDI-TOF MS analysis, the average molecular weight of mono-PEG-sCTs was confirmed as around 8650 Da. The presence of PEG moiety in the mono-PEG-sCTs was also manifested by the fact that the distance between two adjacent mass spectum lines was 44 Da which corresponds to PEG monomer unit. Tryptic digestion analysis demonstrated that these mono-PEG-sCTs are 3 positional isomers of N-terminus, Lys18- and Lys11-residue modified mono-PEGylated sCTs. The degradation half-life of these 3 positional isomers in rat kidney homogenates significantly increased in order of the N-terminus (125.5 min), Lys11- (157.3 min), and Lysl8-residue modified mono-PEGylated sCT (281.5 min) over the native sCT (4.8 min). Conclusions. Three positional isomers of mono-PEGylated sCTs were purified and characterized. Of these, the resistance to proteolytic degradation was highest for the Lysl8-residue modified mono-PEG-sCT. These studies demonstrate that the in vivo stability of PEGylated sCTs is highly dependent on the site of PEG molecule attachment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018861616465
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  • 19
    Electronic Resource
    Electronic Resource
    Phase and aggregation behaviour of double-chain cationic surfactants from the class of N-alkyl-N-alkyl′-N, N-dimethylammonium bromide surfactants (1999)
    Springer
    Colloid & polymer science 277 (1999), S. 856-867 
    Details
    ISSN: 1435-1536
    Keywords: Key words Double chain surfactants ; Aggregates ; Phase diagrams ; Lamellar phases ; Electron microscopy ; SANS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We present the phase diagrams and the properties of newly synthesised double-chain cationic N-alkyl-N-alkyl′-N,N-dimethylammonium bromide surfactants [C x C y DMABr (x = 12, 14 and 16; y = 10, 11, 12, 14 and 16)]. All the systems studied form liquid-crystalline lamellar phases but with different morphologies: unilamellar vesicles at low surfactant concentrations, multilamellar vesicles and tubular aggregates for surfactant concentrations between 2 and 10 wt% and at even higher concentrations planar bilayers of surfactant molecules in the classical Lα phase. The phase diagrams were determined with macroscopic and microscopic methods (polarisation microscopy, freeze-fracture transmission electron microscopy, scanning electron microscopy and differential interference contrast microscopy). The properties of the surfactant solutions were determined with differential scanning calorimetry measurements for Krafft point determination and small-angle neutron scattering measurements for interlamellar spacing and bilayer thickness. Finally, conductivity and viscosity measurements for phase characterisation were carried out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003960050462
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    Synthesis of colloids and films of Pr, Er and Yb with nonaqueous solvents (1999)
    Springer
    Colloid & polymer science 277 (1999), S. 164-173 
    Details
    ISSN: 1435-1536
    Keywords: Keywords Nanostructures ; Thin films ; Vapor deposition ; Electron microscopy ; Optical properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Colloidal dispersions of Yb, Er and Pr have been prepared by chemical liquid deposition. The metals were cocondensed at 77 K with 2-methoxyethanol and ethanol to produce solvated metal atoms. The particle size of the dispersions was determined by transmission electron microscopy to range from 52 to 1080 Å; the particles had spherical shapes. After solvent evaporation under vacuum, active solids and amorphous powder were deposited over Cu and Al metal. Dispersion stability, particle size, UV/Vis absorption and zeta potential were studied. The solids prepared by solvent evaporation were characterized by Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The films prepared on Al were studied by scanning electron microscopy. The most stable colloid was obtained using 2-methoxyethanol: several concentrations were stable for several months and the zeta potential indicated that this colloid stability is mainly due to solvation effects. FTIR spectroscopy of the solids indicated solvent incorporation in the film. This observation was corroborated by thermal analysis. Information on the thermal stability of the films was obtained by TGA. The UV/Vis absorption spectrum was measured at several concentrations under different conditions.
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    URL: http://dx.doi.org/10.1007/s003960050381
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    Determination of ochratoxin a in beer by high-performance liquid chromatography (1999)
    Springer
    Chromatographia 49 (1999), S. 543-546 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; MS-MS detection ; Electrospray-Ionization (ESI) ; Beer ; Ochratoxin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Ochratoxin A (OTA) is a nephrotoxic and nephrocacinogenic mycotoxin commonly produced by several ubiquitousAspergillus andPenicillium species. OTA is found predominantly in cereals and derived products, and therefore OTA may be transferred into beer from contaminated grain. Thirty-five samples of German beers were analyzed: OTA was extracted with toluene and purified by solid phase extraction using silica cartridges. OTA was determined by high-performance liquid chromatography with fluorescence detection. Since of fluorescence detection is not specific in this instance, the beer samples were also analyzed by high-performance liquid chromatography electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS). OTA levels in the range of 0.1–0.2 μg L−1 were found in 9 beer samples, 21 samples contained trace amounts of OTA (〈0.1 μg L−1) and in 5 samples no OTA was detectable.
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    URL: http://dx.doi.org/10.1007/BF02467756
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    Analysis of doxorubicin in cell culture media and human plasma using solid phase extraction and HPLC (1999)
    Springer
    Chromatographia 49 (1999), S. 557-561 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Solid phase extraction ; Doxorubicin ; Cell culture media ; Human plasma ; Fluorescence detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Doxorubicin is an antineoplastic antibiotic isolated fromStreptomyces peucetius var.cesius clinically used in the treatment of tumors such as lung or breast, Hodgkin's disease and various types of leukemias. The main goal of this study was to develop a simple and sensitive HPLC method with fluorescence detection for the quantitation of doxorubicin in cell culture media collected during an in vitro studies and in human plasma. Solid phase extraction (C2 silica) was applied. The experiment established five-point standard curve (1 ng mL−1 to 100 ng mL−1). The standard curves prepared in blank cell tissue media were linear over the range of doxorubicin assayed and had a mean correlation coefficient of 0.9973±9.43×10−4 and slope 0.02545±1.85×10−3. The standard curves prepared in human plasma were linear and had mean correlation coefficient of 0.997 and slope 0.01885±5.19×10−4. The limit of quantitation for doxorubicin in both specimens was arbitrarily established to be 1 ng mL−1. Intra-day variabilities were determined using 3–4 replicates of control solutions of doxorubicin (3 ng mL−1 and 30 ng mL−1) in blank plasma and cell culture media. Inter-day variabilities were determined over a four day period analyzing replicates of controls. All precision and accuracy values fell within the acceptable range.
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    URL: http://dx.doi.org/10.1007/BF02467759
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    Separation of human serum albumin components by RP-HPLC and CZE and their characterization by ESI-MS (1999)
    Springer
    Chromatographia 49 (1999), S. S21 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Capillary zone electrophoresis ; Electrospray ionization-mass spectrometry ; Human serum albumin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Human serum albumin (HSA) is one of the most abundant human proteins and has been shown to be heterogeneous. A RP-HPLC method has been developed to separate HSA components in commercially available preparations. Separations were carried out on Aquapore RP-300, C8 columns using gradient elution with a combination of acetonitrile/water mobile phases containing 0.05% trifluoroacetic acid as ion-pairing agent. Optimum resolution was attained on narrow-bore columns using a stepwise, linear gradient that incorporated a shallow intermediate step of 0.20%/min in Mobile Phase B. Under similar elution conditions, separations carried out on standard-size columns showed the expected decrease in resolution due to increased peak widths. A comparative analysis of three commercial products highlighted qualitative and quantitative differences. Capillary zone electrophoresis was used for the analysis of collected RP-HPLC fractions. Results indicated that while the HPLC separation was incomplete, one of the major HPLC peaks was primarily composed of one of the three main components typically separated by CZE. ESI-MS was used to characterize the two major RP-HPLC fractions and also showed that the HPLC separation was incomplete. The MaxEnt transform of the HPLC peaks was consistent with components all being HSA and closely related derivatives.
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    URL: http://dx.doi.org/10.1007/BF02468972
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    FMOC-Cl as derivatizing agent for the analysis of amino acids and dipeptides by the absolute analysis method (1999)
    Springer
    Chromatographia 49 (1999), S. 317-320 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Amino acids ; FMOC derivatives ; Oligopeptides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary One classical method for quantitation of amino acids in proteins is hydrolysis of the proteins and determination of the free amino acids. Although the drastic experimental conditions necessary for complete hydrolysis always cause degradation of some of the amino acids, if mild hydrolysis conditions are used, a mixture of amino acids and oligopeptides is obtained. If these conditions are adequately tuned, the oligopeptides are almost exclusively dipeptides. For this reason we have initiated a study to find a derivatizing agent suitable for the analysis of amino acids and dipeptides by an absolute method of quantitation already tested for amino acids. FMOC-Cl was found to be a suitable derivatizing agent for this purpose.
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    URL: http://dx.doi.org/10.1007/BF02467563
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    High-performance liquid chromatographic determination/identification of oxytetracycline and sulphadimidine in meat and eggs (1999)
    Springer
    Chromatographia 49 (1999), S. 369-373 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Sep-Pak CN cartridge ; Oxytetracycline ; Sulphadimidine ; Meat and eggs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A rapid method for the simultaneous determination/identification of residual oxytetracycline (OTC) and sulphadimidine (SDD) in meats (beef, pork, chicken) and eggs by high-performance liquid chromatography (HPLC) was developed. The extraction of OTC and SDD was performed using a Sep-Pak® CN cartridge. The extracts contained OTC/SDD analytes when examined by HPLC using a LiChrospher® 100 RP-8 end-capped column and a mobile phase of acetonitrile-acetic acid-water (28:4:68, v/v/v) with a photodiode array detector. The average recoveries from spiked samples (0.1 μg g−1 and 1.0 μg g−1) were in excess of 80.2% with coefficients of variation between 1.5 and 5.0%. The limits of detection for OTC and SDD were 0.05 and 0.02 μg g−1, respectively.
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    URL: http://dx.doi.org/10.1007/BF02467608
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    Improved separation of polyethylene glycols widely differing in molecular weight range by reversed-phase high performance liquid chromatography and evaporative light scattering detection (1999)
    Springer
    Chromatographia 49 (1999), S. 615-620 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Evaporative light-scattering detection ; MALDI-TOF ; Polyethylene glycols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Polyethylene glycols (PEGs) of nominal molecular weight (M) 200, 400, 600, 1000, 1500, 3000, 4000 and 6000 were chosen as model compounds and subjected to reversed-phase high performance liquid chromatography (RP-HPLC) on an octadecasilyl silica gel (C18) stationary phase using a binary gradient composed of acetonitrile and water and evaporative light scattering detection (ELSD). Satisfactory resolution of oligomers up to M of 3000 was accomplished; the higher M samples PEG-4000 and PEG-6000 could not be further resolved into the constituent oligomers and therefore, M=4000 marks the upper limit of oligomer resolution. Despite some peak overlapping as a consequence of the more or less broad oligomer distribution, individual types of PEG samples can be distinguished from each other by their characteristic chromatographic fingerprint patterns, as shown with a mixture consisting of PEG-400, PEG-1000, PEG-3000, PEG-4000 and PEG-6000. For this reason, the method is well-suited for characterization of samples containing PEGs widely differing in M. In addition, matrix assisted laser desorption ionization time of flight mass spectroscopy (MALDI-TOF/MS) performed with PEG-600, PEG-1000 and PEG-3000 revealed that the optimum degree of oligomer resolution has been achieved by use of the present method.
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    Separation of the enantiomers of amino and amide compounds on novel chiral stationary phases derived from a crown ether (1999)
    Springer
    Chromatographia 49 (1999), S. 621-627 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chiral stationary phases ; Crown ether derivatives ; Amino compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The enantiomers of primary amino compounds have previously been resolved on a chiral stationary phase (CSP) CSP-18C6I, prepared by immobilizing (+)-18-crown-6 tetracarboxylic acid. In this study related chiral stationary phases were prepared in an effort to broaden the scope of CSP18C6I. CSP-18C6II, synthesized to investigate the effect of spacer length, resolved the enantiomers of 2-amino-1,2-diphenylethanol and 1-(1-naphthyl)ethylamine (1-NEA) (hydrophobic amino compounds) with the largerk values and smaller α values than on CSP-18C6I, probably because of the greater hydrophobicity of CSP-18C6II. Use of CSP-18C6III, synthesized by modification of carboxylic acid functionality of CSP-18C6II by introduction of another chiral moiety,S-1-NEA, resulted in larger α values for 2-amino-1-phenylethanol and 2-amino-1-phenylpropanol than on CSP-18C6II, but the enantiomers of 1-NEA were not resolved, because of steric hindrance between 1-NEA and the chiral moiety. The amide derivativeN-3,5-dinitrobenzoyl-1-(α-naphthyl)ethylamine (DNN) as π-acceptor (3,5-dinitrobenzoyl function) or π-donor (naphthylethylamide function), and no primary amino functionality, was resolved on CSP-18C6III. The mechanism of separation of the enantiomers of DNN was assumed to be the π−π interaction between the 3,5-dinitrobenzoyl function (π-acceptor) of DNN and theS-1-NEA moiety (π-donor) of CSP-18C6III.
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    URL: http://dx.doi.org/10.1007/BF02466903
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    Determination of alcohols using condensation agent carbazole-9-acetyl-benzene-disulfonate by high performance liquid chromatography with pre-column fluorescence derivatization (1999)
    Springer
    Chromatographia 49 (1999), S. 657-665 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Alcohols ; Pre-column fluorescence derivatization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A sensitive LC method for the determination of alcohols, using fluorescent condensation agent carbazole-9-N-acetylbenzne-disulfonate(CABS), has been developed. A mixture of alcohols and triethylamine catalyst in dichloromethane or chloroform is treated with CABS to give quantitative yields of esters. Emission maximum for the derivatized alcohols is 365 nm (λex 335 nm). The labeled derivatives are very stable, no significant decomposition is observed after heating in 40% at 40°C for 24 h. The method, in conjunction with a multigradient program, offers baseline resolution of common alcohol derivatives on a reversed-phase C18 column. Studies on derivatization conditions indicate that primary and secondary alcohols react very fast with CABS in the presence of triethylamine in dichloromethane or chloroform to give the corresponding fluorescent derivatives. This method is more convenient and more efficient than previous methods which require prior conversion of carboxylic acids to acyl chlorides. The separation of alcohol derivatives has good reproducibility and the rsd's (n=5) for 50 pmol of each alcohol are 4%. Detection limits are at the fmol level.
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    URL: http://dx.doi.org/10.1007/BF02466908
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    Liquid chromatography of jasmonic acid amine conjugates (1999)
    Springer
    Chromatographia 49 (1999), S. 42-46 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chiral resolution ; Jasmonic acid ; Plant growth regulators ; Amine conjugates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Racemic jasmonic acid (3R,7R/3S,7S)-(±)-JA) was chemically conjugated with different biogenic amines originating from aliphatic and aromatic α-amino acids by decarboxylation. The resulting isomeric compounds were subjected to reversed-phase high-performance liquid chromatography (HPLC) and to HPLC on the chiral stationary phases Chiralpak AS and Nucleodex β-PM. Under reversed-phase conditions, all the homologous amine derivatives tested could be separated from each other except the JA-conjugates containing 2-phenyl-ethylamine and 3-methylbutylamine. On both chiral supports the (3R,7R)-(−)-JA conjugates eluted earlier than those of the enantiomeric counterpart (3S,7S)-(+)-JA. On Chiralpak AS all the isomers studied could be separated to baseline with a mobile phase containingn-hexane and 2-propanol. The calculated resolution factors were between 1.80 and 4.17. The pairs of isomers were also chromatographed on the cyclodextrin stationary phase Nucleodex β-PM with methanol-triethylammonium acetate buffer as mobile phase. Under these conditions resolution factors were between 0.74 and 1.29. The individual isomers were chiroptically characterized by measurement of their circular dichroism.
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    Determination of ethinylestradiol and gestodene in oral contraceptives by micellar electrokinetic chromatography (1999)
    Springer
    Chromatographia 49 (1999), S. 65-70 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Micellar electrokinetic chromatography (MEKC) ; Oral contraceptives ; Ethinylestradiol ; Gestodene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A micellar electrokinetic chromatographic method is presented which permits quantification of ethinylestradiol and gestodene in pharmaceutical products. Separation was carried out at 25°C and 25 KV, using a 20 mM borate buffer (pH 9.2), 15 mM sodium dodecylsulfate in 30% acetonitrile-water (v/v). Under these conditions analyses were carried out in 7 min. Four different oral contraceptives were analysed and the results compared favourably with those of a reference liquid chromatographic method.
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    URL: http://dx.doi.org/10.1007/BF02467189
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    Determination of yttrium and lanthanum in zirconium dioxide by HPLC, X-ray fluorescence and neutron activation analyses (1999)
    Springer
    Chromatographia 49 (1999), S. 91-94 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Zirconium oxide ceramics ; X-ray fluorescence ; Neutron activation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Lanthania-and yttria-stabilized zirconium oxide ceramics have been examined using High Performance Liquid Chromatography (HPLC), thermal neutron activation (NA) and X-ray Fluorescence (XRF) analyses and thus determine the stabilizer content. Ceramic powders with the composition ZrO2:x mol % La2O3 (x=5, 10, 15, 20 and 33) and ZrO2:x mol % Y2O3 (x=10, 15, 20 and 25) were prepared by the citrate and the co-precipitation techniques, respectively. The lanthanum content was determined by HPLC (x=5.09, 9.78, 14.98, 19.81 and 25.94) and NA (x=5.15, 10.32, 17.25, 21.08 and 27.97) analyses, the yttrium content by HPLC (x=8.5, 13.5, 17.9 and 22.1) and XRF (x=9.9, 15.8, 20.1 and 24.9) analyses. An experimental sequence, based on continuous dilution of ceramic powder solutions, is proposed for preparing samples for HPLC measurements. A swimming pool nuclear reactor is used for NA analysis. The quantitative determinations of yttrium and lanthanum doping levels obtained using those techniques are described.
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    Stereochemical resolution of racemates, in HPLC, using a chiral stationary phase based upon immobilized α-chymotrypsin. I. Structural chiral separations (1999)
    Springer
    Chromatographia 49 (1999), S. 595-605 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; α-Chymotrypsin immobilized on silica ; In situ immobilization process ; Structural chiral separations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary α-Chymotrypsin was immobilized on an epoxide derivatized silica gel by anin situ immobilization process. Several racemates were resolved by a structural recognition mechanism. The immobilization process and the stability of this α-chymotrypsin stationary phase have been studied. The mobile phase parameters including the ionic strength, pH and the effects of organic modifiers have been also investigated. The retention, efficiency and stereoselectivity of the solutes appear to be related to their molecular structure, hydrophobicity and electrostatic interactions. These relationships determine the recognition mechanism and the position of each enantiomer in the active site.
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    Stereoselective analysis of idrapril and its stereoisomers by reversed-phase high-performance liquid chromatography on a chiral-AGP column (1999)
    Springer
    Chromatographia 49 (1999), S. 628-634 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Enantiomer separation ; Chiral-AGP column ; Idrapril ; Temperature effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A direct liquid-chromatographic method has been developed for the stereoselective analysis of idrapril and its stereoisomers on a chiral α1 glycoprotein (AGP) column. The influence of flow-rate, temperature, and mobile phase composition on retention and selectivity was evaluated to find the optimum conditions for chiral separation.
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    Preparation of branched-polyfluoroalkylsilane-coated silica gel columns and their HPLC separation characteristics (1999)
    Springer
    Chromatographia 49 (1999), S. 649-656 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polyfluoroalkyl-coated silica ; 29Si CP/MAS NMR ; Polyaromatic compounds ; Fluorinated compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The conditions for reaction of the branched polyfluoroalkylsilane D3CL with silica gel have been examined. From elemental analyses and29Si NMR spectra it was found that the surface coverage and endcapping of D3CL-coated silica gel (Fluofix®) were the same as for ODS packings. The separation behavior of these phases was compared that of a variety of other packings. For polyaromatic compounds and benzene derivatives Fluofix worked in the reversed-phase mode and its retention characteristics were similar to those of C1 or CN packings. For fluorinated compound the retention characteristics of the phases is similar to those of ODS although with MeOH-water and MeCN-water mobile phases the pressure loss was lower for the fluorinated phases than for ODS.
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    The effect of pH on the high pH anion-exchange chromatography elution of monosaccharides (1999)
    Springer
    Chromatographia 49 (1999), S. 699-702 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Anion-exchange chromatography ; High ph elvents ; Monosaccharides ; Carbopac PA-100
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary We have studied the elution behaviour of six common monosaccharides, fucose, galactosamine, glucosamine, galactose, glucose and mannose, on the CarboPac PA-100 column. The relative elution positions of galactose, glucose and mannose were dependent on the sodium hydroxide concentrations, a phenomenon which was likely to be the result of differential ionisation of the hydroxyl groups at ring positions two and four. The optimal resolution of the monosaccharides studied was achieved by elution with 30 mM sodium hydroxide with no appreciable loss in sensitivity at this low concentration.
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    High performance liquid chromatography method for the determination of meropenem in human plasma (1999)
    Springer
    Chromatographia 49 (1999), S. 253-255 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Meropenem in human plasma ; Solid phase extraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This paper describes an HPLC method for the determination of meropenem in human plasma. The method uses solid phase extraction (SPE) of the samples and has good sensitivity, precision and accuracy. The limit of quantification in plasma samples is 0.02 μg mL−1. Calibration curves were linear over a large dynamic range, namely within 0.02–50 μg mL−1. The method was applied to the determination of meropenem levels in patients receiving meropenem, as a single dose or at steady state.
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    URL: http://dx.doi.org/10.1007/BF02467552
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    Trace analysis of surfactants derived from fatty alcohols II. Hydrolysis and enrichment techniques (1999)
    Springer
    Chromatographia 49 (1999), S. 12-16 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Fatty alcohol sulfates ; Alkyl polyglycosides ; Trace analysis ; Steam distillation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Acid catalyzed hydrolysis of fatty alcohol sulfates under reflux condition or by microwave heating is compared. Microwave hydrolysis turned out to be faster and more convenient to use. The combination of reflux hydrolysis of fatty alcohol sulfates or alkyl polyglycosides and the simultaneous steam distillation of the generated fatty alcohols gives a very powerful sample preparation and enrichment method for fatty alcohol sulfates and alkyl polyglycosides. The preconcentrated fatty alcohols are derivatized and detected via fluorescence detection. The applicability of the method is demonstrated by the analysis of fatty alcohol sulfates in cosmetics and in river water as matrices spiked with approximately 4 ppb fatty alcohol sulfates.
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    Identification and quantitation of polyphenols in leaves ofMyrtus communis L. (1999)
    Springer
    Chromatographia 49 (1999), S. 17-20 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; DAD and MS detection ; Liquid-solid extraction ; Catechin derivatives ; Myricetin derivatives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A liquid-solid extraction and purification procedure (LSE) was developed to identify and quantify polyphenols in the leaf tissue ofMyrtus communis L. Identification and quantitation of individual compounds was performed using HPTLC, HPLC-DAD and HPLC-MS analysis. Leaves ofMyrtus communis L. contain small amounts of phenolic acids (caffeic, ellagic and gallic acids) and quercetin derivatives (quercetin 3-O-galactoside and quercetin 3-O-rhamnoside), whereas catechin derivatives (epigallocatechin, epigallocatechin 3-O-gallate, epicatechin 3-O-gallate) and myricetin derivatives (myricetin 3-O-galactoside, myricetin 3-O-rhamnoside) are present in large amounts. This is the first report on the occurrence of galloyl-derivatives of catechin and gallo-catechin inMyrtus communis L. leaves.
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    p-Hydroxymercuribenzoate as thiol-protein modifier for simultaneous determination of glycolytic enzymes by hydrophobic-interaction chromatography (1999)
    Springer
    Chromatographia 49 (1999), S. 47-53 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Glycolytic enzymes ; p-Hydroxymercuribenzoate ; 203Hg-labelledp-hydroxymercuribenzoate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The use of hydrophobic-interaction chromatography (HIC) is proposed for the simultaneous determination of more than one thiol-protein after formation of the corresponding mercury mercaptides withp-hydroxymercuribenzoate (PHMB). The new chromatographic procedure, based on the HIC separation of the modified proteins from each other and from excess organomercury reagent has been successfully applied to the quantitative determination of phosphoglucose isomerase (PGI) and phosphoglucose mutase (PGM) in crude PGI powder, and of L-lactate dehydrogenase, PGM and aldolase in crude pyruvate kinase from rabbit muscle. The suitability of203Hg-labelled PHMB has been tested in the analysis of mixtures, which give barely distinguishable UV-peaks owing to the presence of other non-thiol components in the sample. For this purpose glyceraldehyde 3-phosphate dehydrogenase (GAPDHy) and PGIy from bakers yeast have been considered. Results obtained in experiments performed by both procedures are reported.
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    Separation of the enantiomers of amino acid esters as benzophenone imine derivatives on polysaccharide-derived chiral stationary phases (1999)
    Springer
    Chromatographia 49 (1999), S. 61-64 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chiral stationary phases ; Benzophenone imine derivatives ; Amino acid esters ; Enantiomer separation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The liquid-chromatographic separation of the enantiomers of amino acid esters as benzophenone Schiff-base derivatives on polysaccharide-derived chiral stationary phases (CSPs) is described. The performance of Chiralcel OF was superior to that of the other CSPs for resolution of benzophenone imine derivatives of amino acid ethyl and methyl esters. The enantiomers of most of the amino acid esters examined as their benzophenone imine derivatives were resolved to baseline on Chiralcel OF. The L-(−) enantiomers of all the analytes were preferentially retained on Chiralcel OF. The resolution of several imine derivatives of amino acid esters was investigated, as was the effect of eluent composition on the resolution of amino acid ethyl esters as their benzophenone imine derivatives.
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    Development and validation of an HPLC method for the simultaneous determination of clozapine and desmethylclozapine in plasma of schizophrenic patients (1999)
    Springer
    Chromatographia 49 (1999), S. 75-80 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Amperometric detection ; Clozapine ; Desmethylclozapine ; Drug monitoring
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A high-performance liquid chromatographic method with amperometric detection has been developed for the determination of levels of clozapine (CLZ) and its active metabolite N-desmethylclozapine (DMC) in human plasma. The analysis was performed on a 5 μm C8 reversed phase column (150×4.6 mm i.d.), with acetonitrile-phosphate buffer (pH 3.5), as the mobile phase. The detection voltage was +800 mV and the cell and column temperature were 50°C. Linear responses were obtained between 2 ng mL−1 and 100 ng mL−1. Absolute recovery for both clozapine and desmethylclozapine exceeded 88% and the detection limit was 1 ng mL−1. Repeatability, intermediate precision and accuracy were satisfactory. The method, which is rapid, sensitive and selective, has been applied to therapeutic drug monitoring in schizophrenic patients following administration of Leponex® tablets. In 21 patients in steady state at a mean daily clozapine dosage of 358 mg (ranging from 150 to 500 mg day−1), clozapine levels averaged 379 ng mL−1 (ranging from 102 to 818 ng mL−1) and DMC levels averaged 233 ng mL−1 (ranging from 70 to 540 ng mL−1). The method requires only a very small amount of plasma (100 μL), and thus it is suitable for pharmacokinetic studies, as well as for therapeutic drug monitoring.
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    Study of the chromatographic behavior and inclusion constants of new fluorescence agents by use of cyclodextrin additives under conditions of steady- and dynamic-state equilibrium and with fluorescence detection (1999)
    Springer
    Chromatographia 49 (1999), S. 95-104 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Cyclodextrin additives ; Fluorescence agents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary We report four new derivatization agents, acridone-N-acetic acid (ARC), carbazole-9-ylacetic acid (CRA), carbazole-9-ylpropionic acid (CRP), and 2-methyl-2-carbazole-9-ylacetic acid (MCRA), with strong fluorescence emission which has low dependence on solvent polarity. The emission maxima for ARC, CRA, CRP, and MCRA were 430 nm (λex 404 nm), 368 nm (λex 335 nm), 356 nm (λex 340 nm) and 360 nm (λex 330 nm), respectively. The effects of mobile-phase composition, pH, and temperature on the liquid chromatographic retention behavior of the four fluorescence agents were investigated. An experimental model was established for calculating the inclusion constants of cyclodextrin (CD) complexes in the dynamic state, using β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) as examples, and different mobilephase compositions. On the basis of the model, the inclusion constants of the solutes in pure water (K fw) were determined by extrapolation. The thermodynamic parameters (ΔH o and ΔS o) and dissociation constantsK am for the solutes in this chromatographic system were obtained by means of capacity factor (k) values using a corresponding model formulation.
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    Effect of triethylamine in the mobile phase on the retention properties of conventional polymeric and horizontally polymerized octadecylsilica in RPLC (1999)
    Springer
    Chromatographia 49 (1999), S. 635-642 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Interaction of mobile and stationary phases ; Linear solvation energy relationships ; Triethylamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The effect of triethylamine (TEA) in the mobile phase on the RPLC retention behavior of small organic solutes has been studied on a conventional polymeric octadecylsilica (ODS) and on a horizontally polymerized ODS. Retention factors for a set of solutes were measured on the two phases with methanol-water mobile phases containing triethylamine at different concentrations and analyzed by use of linear solvation energy relationships (LSER). Variation of the resulting LSER coefficients—v (hydrophobicity),r (polarizability),s (dipolarity),b (hydrogen-bond (HB) donating acidity), anda (HB accepting strength)—were examined to see how TEA affects the intermolecular interaction properties of the mobile and stationary phases and hence the retention of the solutes. Addition of TEA to the mobile phase changes the interaction properties of both conventionally polymerized and horizontally polymerized ODS; the effect is greater for the conventional phase. The HB donating acidity (b) of conventional polymeric ODS is significantly reduced by addition of TEA. For the mobile phases studied the magnitudes of theb andv coefficients for the horizontally polymerized ODS phase are greater than for the conventional phase. The different interaction properties of the two polymeric phases arise mainly as a result of differential adsorption of TEA, because of the very different amounts of surface silanol groups present on the two phases.
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    Preparation and evaluation ofp-tert-butyl-calix[4]arene-bonded silica stationary phases for high performance liquid chromatography (1999)
    Springer
    Chromatographia 49 (1999), S. 643-648 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; p-tert-Butyl-calix[4]arene-bonded silica ; Nuclear magnetic resonance spectrometry ; PAHs ; Nucleosides bases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new method is proposed for preparation of ap-tert-butyl-calix[4]arene-bonded silica stationary phase. The chemically modifiedp-tert-butyl-calix[4]arene is attached to silica gel via the silane coupling reagent γ-(ethylenediamino)-propyl-triethoxyl-silane. The bonded phase has been characterized by29Si and13C cross polarization/magic angle spinning solid-state nuclear magnetic spectrometry. The retention behavior of polycyclic aromatic hydrocarbons (PAHs), nucleosides and bases has been investigated on the bonded phase in the reversed-phase mode.
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    Hydrolysis of microcystins and nodularin by microwave radiation (1999)
    Springer
    Chromatographia 49 (1999), S. 671-677 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Microwave hydrolysis ; Microcystin ; Nodularin ; D- and L-selective amino acid determination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Microwave radiation has been successfully used for hydrolysis of the hepatotoxic cyclic peptides microcystins and nodularin. Set-up of the microwave device and the operating conditions for microwave hydrolysis were optimized. Results of the microwave hydrolysis were compared with results from conventional hydrolysis for 24 h at 110°C. Microwave hydrolysis of microcystins and nodularin for as little as 10 min at 160°C results in complete cleavage of peptide bonds and high recoveries of amino acids. Enantioselective determination of amino acids was achieved by use of a previously described HPLC method after pre-column derivatization withortho-phthaldialdehyde and the chiral thiolN-iso-butyryl-cysteine.
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    Peculiarities of the mechanism of retention of imidazole derivatives when using hydroxypropyl-β-cyclodextrin as mobile phase additive (1999)
    Springer
    Chromatographia 49 (1999), S. 691-698 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Hydroxypropyl-β-cyclodextrin ; Imidazole derivatives ; Retention mechanisms ; Enthalpy-entropy compensation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Two different methods have been used to investigate the retention mechanism of a series of imidazole derivatives in reversed-phase liquid chromatography (RPLC) over a range of column temperatures and with different concentrations of hydroxypropyl-β-cyclodextrin (HP-β-CD) in the mobile phase. The first approach was the separate study of each factor affecting the retention mechanism; the second method was the simultaneous variation of all these factors. Changes in Van't Hoff plots as a function of HP-β-CD concentration were examined. Enthalpy and entropy were determined for two physicochemical processes: (i) solute transfer from the mobile phase to the stationary phase, and (ii) solute complexation by HP-β-CD. These thermodynamic data showed that the mechanism of retention of the solute was dependent on the concentration of HP-β-CD in the mobile phase. For a HP-β-CD concentration,C, greater than to 4 mM, from 28°C to a critical temperature,T *, solute retention was entropy-dominated because of inclusion of the solute in the HP-β-CD cavity. AboveT * retention was enthalpy-dominated, because of interaction of the solute with the RP18 stationary phase. At firstT * increased asC was increased up to a critical value,C **; it the remained relatively constant because of auto-association of the HP-β-CD molecules in the mobile phase. Enthalpy-entropy compensation revealed that HP-β-CD-solute complexation had a greater effect on retention than RP18 stationary phase-solute interaction. This confirms that the main parameter determining retention in RPLC is the distribution of the solute in the mobile phase, and that interactions with the stationary phase play a minor role.
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    Analysis of commercial ceramides by non-aqueous reversed-phase liquid chromatography with evaporative light-scattering detection (1999)
    Springer
    Chromatographia 49 (1999), S. 241-248 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Non-aqueous reversed-phase liquid chromatography ; Evaporative light-scattering detection ; Octadecyl grafted silica ; Ceramides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This paper describes the development of a chromatographic system for analysis of commercial ceramides structurally similar to those found in the stratum corneum. The ceramides used in this study contain different amine based (phytosphingosine, sphingosine and dihydrosphingosine) and fatty acids of different chain lengths and with different functional groups (hydroxylated and unsaturated). Non-aqueous reversed-phase (NARP) liquid chromatography with evaporative light-scattering detection (ELSD) were the techniques chosen in accordance with the nature of the ceramides. The eluent strength and the potential selectivity of different organic solvents were investigated. On a C18-bonded silica, the most promising chromatographic conditions employed a gradient from ACN-THF, 95∶5, to ACN-THF-PrOH, 35∶5∶60, in 15 min with a constant concentration of TEA (10 mM) and a stoichiometric amount of formic acid.
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    High-performance liquid chromatographic method for separation and quantification of intact glucosinolates (1999)
    Springer
    Chromatographia 49 (1999), S. 281-284 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Glucosinolates ; Rapseed-mustard ; Brassica
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple, economical and efficient HPLC method has been developed for the separation and determination of the individual glucosinolates in rapessed and mustard. The method involves single-step extraction of glucosinolates with boiling water and separation of the individual glucosinolates on a Novapack RP-18 column (3.9 mm ×150mm) with 0.2 M ammonium sulphate as mobile phase. Peaks were monitored at 229 nm. All major glucosinolates could be eluted within 10 min. The method proved effective for routine analysis of glucosinolates.
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    Determination of flupoxam residues in soil by high performance liquid chromatography (1999)
    Springer
    Chromatographia 49 (1999), S. 535-538 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Solid phase extraction ; Herbicides in soil ; Flupoxam
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary High-performance liquid chromatography with UV detection was used to determine the residues of flupoxam (a new herbicide) in soils. Soil samples were extracted with aqueous methanol. The soil extracts were cleaned up and concentrated using two solid phase extraction columns: a polymeric stationary phase based on a polystyrene-divinylbenzene resin (Lichrolut EN) and alumina. Recovery experiments were performed at ppb levels in spiked soil samples. The recovery was 76±1.7% for flupoxam in the range 5–100 μg kg−1 of soil. Limit of determination was 3 μg kg−1.
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    Stereochemical resolution of racemates, in HPLC, using a chiral stationary phase based upon immobilized α-chymotrypsin. II. Enzyme chiral separations (1999)
    Springer
    Chromatographia 49 (1999), S. 606-614 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; α-Chymotrypsin-CSP ; Enzymatic chiral separations ; Loadability evaluation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Several racemates has been resolved according to an enzymatic recognition mechanism on an α-chymotrypsin chiral stationary phase. The loadability of the ACHT-CSP has been evaluated both in buffered and non-buffered mobile phases under the enzymatic process and compared with the loading capacity obtained by the structural recognition process.
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    HPLC resolution of the enantiomers of glycidyl sulfides and glycidyl selenides on amylose tris-(phenylcarbamate) stationary phase (1999)
    Springer
    Chromatographia 49 (1999), S. 572-574 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Enantioseparations ; Amylose phenylcarbamate phase ; Glycidyl sulfides ; Glycidyl selenides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The resolution of the enantiomers of a series of glycidyl sulfides and glycidyl selenides has been examined on a chiral stationary phase prepared by coating aminopropylated silica gel with amylose tris-(phenylcarbamate). Most of the enantiomers of glycidyl monosulfides and monoselenides could be resolved satisfactorily but those of the disulfides could not. The effects of solute structure and of the concentration of 2-propanol in the mobile phase on retention and resolution were investigated.
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    Determination of cisplatin, transplatin and amminetri-chloroplatinate by high performance liquid chromatography in one run using 4-methyl-2-thiouracil as derivatizing agent (1999)
    Springer
    Chromatographia 49 (1999), S. 562-566 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Cis-diamminedichloroplatinum (II) ; Transdiamminedichloroplatinum (II) ; Amminetri-chloroplatinate ; 4-Methyl-2-thiouracil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary We have developed a simple, rapid, selective and sensitive method for detecting the antitumour agent cis-diamminedichloroplatinum (II) (cisplatin) (CDDP) and its toxic impurities trans-diamminedichloroplatinum (II) (transplatin) (TDDP) amminetri-chloroplatinat (ATCP) anion using HPLC in one run. By using 4-methyl-2-thiouracil (MTU) as a derivatizing agent, new compounds have been formed from the Pt compounds and separated on a μ-Bondapak C18 column with isocratic elution and detection at 315 nm. Reactant concentration, methanol content, pH and the reaction time on yield of derivatives were investigated and the optimum conditions for the detection response were defined. The derivatives of each of the three platinum compounds formed in an acetate buffer solution containing 40% (v/v) methanol and 0.9% KCl solution at pH 3.7 and ambient temperature were only stable for one hour.
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    Unexpected behavior of digoxin at elevated temperatures in reversed-phase liquid chromatography (1999)
    Springer
    Chromatographia 49 (1999), S. 306-308 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Digoxin and digoxigenin ; Temperature effects ; Pore size effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Increased retention of digoxin has been observed at elevated temperatures on both 10 nm and 30 nm porediamter, RP-18 packing. This result is the opposite effect compared with the decreased retention under the same conditions with digoxin aglycon-digoxigenin. Rotation around the C−C σ-bonds in the digoxin molecule is presumed; the rod-like molecules of the newlyobtained digoxin penetrate stationary phase pores more easily thus increasing retention.
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    Potentiometric detection of monovalent anions separated by ion chromatography using all solid-state contact PVC matrix membrane electrode (1999)
    Springer
    Chromatographia 49 (1999), S. 338-342 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion chromatography ; Monovalent anions determination ; Potentiometric detection ; Ion selective PVC-matrix electrode
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An all solid-state contact tubular PVC-matrix membrane electrode has been applied for potentiometric detection of inorganic and organic monovalent anions using phosphate and hydrogen phosphate eluents at low concentrations. This is a “monovalent detection method” as the selectivity of the electrode towards monovalent anions results in some other anions being undetected unless the concentration of those other anions is higher than 10−3 mol dm−3 in the sample solution injected. It takes only eight minutes to complete the separation with a good resolution. Theoretical and practical considerations are discussed, and in particular, sensitivity, linearity, detection limit and dynamic behaviour are presented. The use of an all solid-state contact bromide-selective electrode as a detector offers so far the best simultaneous sensitivity toward all anions when compared with other detection methods. Determination of Cl− and NO3 − ions in river, rain and drinking water samples without any further sample preconcentration has been successfully achieved. The detection limit is sub-ppb for most of anions in a 20 μL injection volume.
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    Normal-phase high performance liquid chromatographic separation and characterization of short- and long-chain triacylglycerols (1999)
    Springer
    Chromatographia 49 (1999), S. 363-368 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Evaporative light scatering detection ; APCI mass spectrometry ; Triacylglycerols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Short- and long-chain triacylglycerols (SLCT) are a family of lipids prepared by chemical or enzymatic interesterification of triacetin, tripropionin and/or tributyrin, and long-chain (C16!18) hydrogenated vegetable oils. In this study, a normal-phase cyanopropyl high-performance liquid chromatographic (HPLC) method was developed for the separation and quantification of SLCT. The method is capable of separating SLCT mixtures, free fatty acids and the neutral lipid classes of saturated long-chain triacylglycerols, diacylglycerols and monoacylglycerols. To characterize the specific SLCT classes, a normal-phase HPLC procedure using a non-modified silica column was developed to separate the SLCT into individual isomers based on total carbon number and position of fatty acids on the glycerol backbone. Online coupling with a mass detector (LC/MS) allowed the identification of the individual triacylglycerol structures.
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    Comparison of octadecyl bonded titania phases (1999)
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    Chromatographia 49 (1999), S. 424-430 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Octadecyl titania ; Surface hydrosilation ; Solid-state NMR C7
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The structure of a C18 phase based on titania (C18-A), synthesized by the method of solution polymerization, is investigated by diffuse reflectance infrared Fourier transform (DRIFT) and solid-state nuclear magnetic resonance (NMR) spectroscopy. The findings are compared with the results of a second C18 phase based on titania (C18-B) which was synthesized by the method of surface hydrosilation. The dynamic behavior of both phases is examined by1H MAS NMR detection of spinlattice relaxation times in the rotating frame (T1pH) and conventional spin-lattice relaxation times (T1). Due to a smaller ligand density, phase C18-A appears to be a somewhat more mobile than phase C18-B. The chromatographic capability of the phase C18-A is demonstrated by the separation of samples containing benzene derivates or anilines. The elution order is analogous to the phase C18-B, but for both test mixtures the polarity of the mobile phase has to be increased. Phase C18-A is classified as being polymeric by the Sander and Wise test, whereas phase C18-B shows intermediate retention behavior.
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    High performance liquid chromatography coupled to nuclear magnetic resonance spectroscopy and mass spectrometry applied to plant products: Identification of ecdysteroids fromSilene otites (1999)
    Springer
    Chromatographia 49 (1999), S. 374-378 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; NMR spectroscopy and mass spectrometry ; Plant products ; Silene otites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary HPLC coupled in parallel to nuclear magnetic resonance (NMR) and mass spectrometry (MS) has been used to obtain1H NMR and mass spectra of a number of ecdysteroids present in an extract of the plantSilene otites. Reversed phase gradient chromatography was performed using a D20-acetonitrile-based solvent system. NMR and mass spectra were obtained for integristerone A, 20-hydroxyecdysone, 2-deoxy-20-hydroxyecdysone and 2-deoxyecdysone to provide structural confirmation using continuous and stopped flow HPLC-NMR. The combined HPLC-NMR-MS system described here provided a more comprehensive analysis of the ecdysteroids present in the extract than HPLC-NMR alone.
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    A system for predicting the retentions of O-alkyl, n-(1-methylthioethylideneamino) phosphoramidates on RP-HPLC (1999)
    Springer
    Chromatographia 49 (1999), S. 444-448 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; O-alkyl, O-(1-methylthioethylideneamino) phosphoramidates ; Quantitative structure-retention relationship (QSRR) ; Reversed-phase LC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary By using factor analysis, cluster analysis and multiple linear regression methods, two parameters, FHF and ECCR, were selected from eight solute-related structure parameters as showing the best correlation with retention data. The relationship between the retention data (k) and these two structure parameters were established for ten O-alkyl, O-(1-methylthioethylideneamino) phosphoramidate compounds under the experimental conditions studied. Retention data (k) for six other compounds that have a high correlation with structure parameters were predicted using these QSRR equations. The system was evaluated by comparing the experimentalk values with the predicted ones. Good agreement was obtained between the experimental and predictedk values.
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    The effect of Li and La on NiO/Al2O3 catalyst for CH4/O2 to syngas reaction (1999)
    Springer
    Reaction kinetics and catalysis letters 68 (1999), S. 243-247 
    Details
    ISSN: 1588-2837
    Keywords: Methane partial oxidation ; nickel-based catalysts ; stability ; sintering and loss of nickel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The thermal stability and an 80 h life test over nickel-based catalysts for CH4/O2 to syngas reaction were investigated by flow-reactor, XPS, XRD and AAS analysis. The results indicate that the introduction of Li and La not only stabilized the support γ-Al2O3 phase, but also suppressed the sintering and loss of nickel, and in addition, enhanced the ability to suppress the carbon-deposition over NiO/Al2O3 during the high-temperature reaction.
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    Binding and Ionophoric Properties of Polythioamide Compounds. Ag(I) and Hg(II) Selectivities (1999)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 34 (1999), S. 277-289 
    Details
    ISSN: 1573-1111
    Keywords: complexes ; stability ; extraction ; transport ; tetrathiolactams
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The synthesis of tetrathiolactams and related di- and tetrathioamide compounds is described. The formation constants of their heavy-metal complexes are determined by using the strong UV absorption of the thioamide chromophore. Extraction and transport abilities of tetrathioamide ionophores show selectivities for Ag(I) and Hg(II) cations over alkali, alkaline-earth or other heavy metal cations including transition metals such as Co(II).
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    URL: http://dx.doi.org/10.1023/A:1008093510236
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    Polarographic Studies on Anion Coordination Chemistry. Host–Guest Interactions of Hexacyclen and Pentacyclen with Pyrophosphate, Selenite, Selenate, Molybdate and Tungstate Anions (1999)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 34 (1999), S. 455-464 
    Details
    ISSN: 1573-1111
    Keywords: hexacyclen ; pentacyclen ; anion complexes ; stoichiometry ; stability ; polarography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The complexation of protonated hexacyclen and pentacyclen with pyrophosphate, selenite, selenate, molybdate and tungstate anions was studied by differential pulse polarography at 25 °C. The stoichiometry and stability of the resulting anion complexes were evaluated from the pH and concentration-dependence of the peak potentials, respectively. The results established 1 : 1 anion receptor complexation in all cases. In the case of all anions studied, hexacyclen was found to form more stable anion complexes than pentacyclen. The fact that the anion-receptor complexation depends on the structural features of both the anions and the macrocycles used is indicative of a steric controlled interaction.
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    URL: http://dx.doi.org/10.1023/A:1008050909119
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    Ethene hydroformylation on Co/SiO2 catalysts (1998)
    Springer
    Catalysis letters 53 (1998), S. 97-101 
    Details
    ISSN: 1572-879X
    Keywords: ethene hydroformylation ; heterogeneous catalysts ; cobalt catalysts ; gas‐phase deposition ; dispersion ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The results from ethene hydroformylation at 173°C showed that a Co(acac)3/SiO2 catalyst prepared from Co(acac)3 precursor by gas‐phase deposition was three times as active as a catalyst prepared by impregnation from cobalt nitrate, but oxo‐selectivities were similar. The high propanal selectivities on the Co(acac)3/SiO2 seem to be related to the presence of highly dispersed active sites favouring CO insertion. As dispersion is decreased from 23 to 8% due to increasing metal content (from 5 to 16 wt%), oxo‐selectivity decreased from 39 to 25%. The activity of Co(acac)3/SiO2 remained unchanged during 68 h on stream. The gas‐phase deposition technique described here is a promising method for the preparation of active, selective and stable heterogeneous hydroformylation catalysts.
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    URL: http://dx.doi.org/10.1023/A:1019053805618
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    Preparation of model catalysts by laser interference nanolithography followed by metal cluster deposition (1998)
    Springer
    Catalysis letters 56 (1998), S. 1-6 
    Details
    ISSN: 1572-879X
    Keywords: nanolithography ; model catalyst ; palladium ; copper ; stability ; spin-coating ; SEM ; AFM ; XPS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Metal clusters arranged on nanostructured oxidized silicon wafers are presented as new model catalyst systems. A photoresist layer spun on top of a wafer was patterned by laser interference exposure. The grid obtained after removing the exposed parts of the resist is used as an etching mask. Hollows with diameters of 300 nm and depths between 50 and 60 nm were etched into the oxide layer using wet chemical methods. Two methods were applied to deposit metal clusters (Pd or Cu) in a defined way within the hollows. The particles ranged from 10 to 50 nm in height and from 80 to 200 nm in diameter. The model catalyst systems were characterized by atomic force microscopy and X-ray photoelectron spectroscopy. The method presented here allows us to produce 4 inch wafers that are covered completely by nanometer-sized structures in a reasonable period of time.
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    URL: http://dx.doi.org/10.1023/A:1019080222823
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    Pharmaceutical development of a parenteral lyophilized formulation of the investigational antitumor neuropeptide antagonist [Arg6, D-Trp7,9, MePhe8]-Substance P {6-11} (1998)
    Springer
    Investigational new drugs 16 (1998), S. 99-111 
    Details
    ISSN: 1573-0646
    Keywords: Antagonist G ([Arg6, D-Trp7,9,,MePhe 8 ]-Substance P {6-11}) ; analytical characterization ; parenteral formulation ; stability ; oxidative degradation products
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Abstract The aim of this study was to develop a stable parenteral dosage form for the investigational cytotoxic drug [Arg6, D-Trp7,9, MePhe8]-Substance P {6-11} (Substance P Antagonist G; Antagonist G). Antagonist G bulk drug was structurally and analytically characterized. The drug exhibits excellent aqueous solubility, although relatively poor aqueous stability characteristics. Lyophilization was, therefore, selected as the manufacturing process. Differential scanning calorimetry studies were conducted to determine the freeze-drying cycle parameters which resulted in a stable, lyophilized formulation of Antagonist G. The prototype, containing 50 mg Antagonist G per vial, was found to be the optimal formulation in terms of solubility, length of the freeze-drying cycle, stability, and dosage requirements in the planned phase I clinical trials. Quality control of the freeze-dried formulation showed that the manufacturing process does not change the integrity of Antagonist G. Shelf life studies demonstrated that the formulation is stable for at least 3 years, when stored at 2–8°C in a dark environment. Oxidative degradation products of Antagonist G were isolated and structurally characterized by mass spectrometry, nuclear magnetic resonance spectroscopy, and infrared spectroscopy.
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    URL: http://dx.doi.org/10.1023/A:1006041024109
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    Isothermal and Nonisothermal Decomposition of Thymopentin and Its Analogs in Aqueous Solution (1998)
    Springer
    Pharmaceutical research 15 (1998), S. 1702-1707 
    Details
    ISSN: 1573-904X
    Keywords: stability ; isothermal ; nonisothermal ; thymopentin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The degradation kinetics of thymopentin (RKDVY) and its analogs (RKDVW and RPDVY) in aqueous solution was studied by isothermal and nonisothermal methods. Methods. The isothermal decomposition of thymopentin and its analogs was investigated as a function of pH (2−10), temperature (37, 57, and 80°C) and ionic strength (μ = 0.02 to 1). Nonisothermal decomposition studies were performed using a linear temperature programmer. The temperature increasing rate was set to 0.25°C per hour and the temperature interval varied from 40 to 88°C. Results. The decomposition of thymopentin and its analogs followed first order kinetics. The dependence of the rate constant on temperature followed a linear Arrhenius plot. This indicated that the degradation mechanism of thymopentin and its analogs might be the same within the temperature range studied. The energies of activation were found to be in close agreement for the isothermal and nonisothermal studies, suggesting that the nonisothermal studies may save considerable amount of time in the early stages of drug development. The logK-pH profile of thymopentin suggests that maximum stability is achieved in the pH range of 6−8. Conclusions. These results indicate that the nonisothermal methodology provides an attractive alternative to isothermal methods, as it requires a much lower amount of both material and time, to determine the peptide stability and to estimate the shelf-life for peptide pharmaceutical preparations.
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    URL: http://dx.doi.org/10.1023/A:1011952511091
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    The synthesis of polymer suspension with narrow particle size distribution for immunochemical investigations (1998)
    Springer
    Colloid & polymer science 276 (1998), S. 1068-1077 
    Details
    ISSN: 1435-1536
    Keywords: Key words Heterophase polymerization ; emulsion ; polymer particle ; stability ; styrene conversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  Heterophase polymerization of styrene in the presence of di-p-tolyl-o-carbalkoxyphenylcarbinol (DTC) soluble in monomer and insoluble in water, as stabilizer, was investigated. The factors affecting polymer particle diameter, their size distribution and stability were investigated. It was suggested that polymer particles are formed from monomer droplets. The polystyrene suspension with narrow particle size distribution synthesized in the presence of DTC, was used for immunochemical research.
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    URL: http://dx.doi.org/10.1007/s003960050348
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    Application of SPE for the HPLC analysis of taxanes fromTaxus cell cultures (1998)
    Springer
    Chromatographia 47 (1998), S. 25-34 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Solid Phase Extraction ; RP-HPLC gradient analysis ; Taxus Cell Cultures ; Taxol and Taxanes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Solid phase extraction (SPE) methods are studied for the sample pretreatment for HPLC analysis ofTaxus cell suspension cultures. Various types of SPE materials were tested for the extraction of both the taxane standards and samples of various origin. Comparison between the different cartridges and the different elution solvents are made in terms of extraction recovery and sample clean-up. Selective elution of the taxanes is achieved by a gradient elution scheme.
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    URL: http://dx.doi.org/10.1007/BF02466782
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    Ionic strength dependence of heavy metal tartrate complex stabilities (1998)
    Springer
    Chromatographia 47 (1998), S. 77-80 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion chromatography ; Stability constants ; Ionic strength ; Heavy metals ; Tartaric acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Ion chromatography and potentiometry were used for the determination of the stability constants Pb, Zn, Co, Ni, Mn tartrate complexes at different ionic strengths. An extrapolation function based on the Debye-Hückel equation was applied to obtain the thermodynamic stability constants.
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    URL: http://dx.doi.org/10.1007/BF02466789
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    Development of an Ion-pair HPLC method for the determination of 2,4- and 2,6-toluendiamine in human plasma (1998)
    Springer
    Chromatographia 47 (1998), S. 84-88 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-pair LC ; Plasma ; 2,4-Toluendiamine ; 2,6-Toluendiamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An ion-pair HPLC method is presented for the determination in plasma of 2,4- and 2,6-toluendiamine (TDA), known carcinogens. The chromatographic conditions consisted in isocratic elution on a reversed phase C18 column with 5 mM octanesulfonic acid in methanol-water, 45∶55, as mobile phase. UV detection was performed at 235 nm. Samples were analyzed after a simple single step liquid-liquid extraction and the method was validated by measurement of precision (interassay and intraassay), sensitivity, specificity, linearity, and recovery. The detection limit for both TDAs in plasma was 20 ng mL−1. The correlation coefficients based on the intrassay calibration curve were 0.998 and 0.997 for 2,6- and 2,4-TDA, respectively. The intraassay accuracy, expressed in terms of recovery, was found to be up to 89.91% and 97.05% for 2,6- and 2,4-TDA, respectively.
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    URL: http://dx.doi.org/10.1007/BF02466791
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    Direct resolution of a new antifungal agent, voriconazole (UK-109,496) and its potential impurities, by use of coupled achiral-chiral high-performance liquid chromatography (1998)
    Springer
    Chromatographia 47 (1998), S. 649-654 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Enantiomer separation ; Voriconazole (UK-109,496) ; Effect of organic mobile-phase modifier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Coupled achiral-chiral high-performance liquid chromatography (HPLC) with an achiral amino-based column coupled with a chiral amylose-based column has been used for qualitative and quantitative determination of the potential chiral and achiral impurities of Voriconazole (UK-109,496), a new antifungal agent with two stereogenic centres. The effect of the organic mobile-phase modifier, ethanol, was studied. The assay response was linearly dependent on concentration over the range 1.2–40.4 μg for Voriconazole and 2.5–104.0 ng for the impurities. The limit of detection was 2.5 ng for each analyte.
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    Separation of inorganic anions and cations on titania by use of acetic acid-sodium acetate and bicine-sodium hydroxide buffers (1998)
    Springer
    Chromatographia 47 (1998), S. 655-658 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion chromatography ; Titania packings ; Inorganic anions and cations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The ion-exchange retention behavior of titania synthesized in our laboratory was investigated by ion chromatography of inorganic anions and cations. Dilute acetic acid-sodium acetate and bicine-sodium hydroxide buffers were used as mobile phases with no use of suppresor. We observed that the titania, although poor at separating monovalent anions expcept nitrite ion in this experiment, was both an anion and a cation exchanger, and selectively retained fluoride and carbonate ions. We concluded that because of its specific retention properties there were possibilites of using this amphoteric exchanger for simultaneous analysis of anions and cations, and of using it as a selective packing material for ion chromatography.
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    Retention behavior of morphine and its metabolites on a porous graphitic carbon column (1998)
    Springer
    Chromatographia 47 (1998), S. 667-672 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Porous graphitic carbon ; Optimization ; Morphine and metabolites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The chromatographic behaviour of a series of morphine-based opiates has been investigated using a porous graphitic carbon packing material at acid and alkaline pH. The effects of mobile phase pH, mobile phase organic percentage, column temperature and ionpairing agents were studied. All six opiates were separated within a close retention window despite large differences in measured lipophilicities of the individual opiates. The retention order was not related to the log P values of the opiates and strong retention of the fully ionised compounds was observed, particularly those with acidic functional groups. The effect of pH on the retention of the compounds indicated that the degree of ionisation of the individual compounds was important in the separation mechanism, suggesting that hydrophobic interactions were present in addition to the polar retentive effects observed above. The strong retention of the ionised glucuronide and sulphate conjugates of morphine is a particularly useful feature of the porous graphitic carbon packing material which has general applicability to the analysis of polar or ionised drug metabolites.
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    URL: http://dx.doi.org/10.1007/BF02467451
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    Determination of clozapine in human plasma by solid-phase extraction and liquid chromatography with amperometric detection (1998)
    Springer
    Chromatographia 47 (1998), S. 8-12 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Amperometric detection ; Solid-phase extraction ; Plasma ; Clozapine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A sensitive and selective high-performance liquid chromatographic method has been developed for monitoring clozapine levels in human plasma. Chromatography was performed on a reversed-phase column (C8, 150 mm×4.6 mm i.d., 5 μm) with acetonitrile-aqueous sodium acetate solution, 88∶12 (v/v), as mobile phase; the flow rate was 1 mL min−1. Clozapine oxidation at +800 mV was detected amperometrically. Response was linearly dependent on concentration over the range 50–1500 ng mL−1 clozapine in plasma. Sample preparation by solid-phase extraction before HPLC analysis gave high extraction yield (94%). The accuracy and precision of the method were both very good (recovery: 97%;RSD〈3.3%).
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    URL: http://dx.doi.org/10.1007/BF02466779
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    Characterization of the precolumn bio trap 500 C18 for direct injection of plasma samples in a column-switching system (1998)
    Springer
    Chromatographia 47 (1998), S. 299-304 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Plasma samples ; Direct injection ; Restricted-access media ; Column-switching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new restricted access media (RAM) type of precolumn, Bio Trap 500 C18, for direct injection of plasma samples in column-switching systems was evaluated with respect to the elution of plasma proteins in different mobile phases, the loading capacity of plasma samples, the chromatographic behavior during plasma injections and protein contamination of the packing and sealings. More than 95% of plasma proteins could be excluded from the precolumn within three minutes for all selected mobile phases. Quantitative analyte recoveries could be obtained by injecting plasma samples ranging from 5 to 500 μL with the analyte mass〉150 ng onto a BioTrap 500 C18 column (20×4 mm I.D.). One precolumn tolerated about 15 mL of plasma injection without out noticeable change in retention and pressure. Clogging of the precolumn was encountered (≥45 mL of plasma) due mainly to the adsorption of proteins on the packing. The performance of the analytical column (Kromasil C18) was also examined. The column efficiency decreased by 60% after processing 45 mL plasma in total.
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    Characterisation of pitch by HPLC (1998)
    Springer
    Chromatographia 47 (1998), S. 373-382 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polyaromatic hydrocarbons ; Pitch
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new high performance liquid chromatography method for the characterisation of toluene-soluble fractions of pitches has been developed. Although a chromatographic system typical of size exclusion chromatography was used, results indicate that, for these structurally complex samples, separation does not follow the usual discrimination by molecular size. A differentiation between several classes of polyaromatic hydrocarbons is achieved instead. Data are reported on the analysis of individual standard polyaromatic hydrocarbons, showing that four different elution ranges can be observed: three ofcata-condensed compounds (Cata1, Cata2 and Cata3) and one ofperi-condensed compounds (Peri). Results are reported proving the capacity of this high performance liquid chromatography method to distinguish between pitches of different origin and nature. It is also effective for the study of the chemical reactions occurring during heat treatment.
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    Determination of the five major opium alkaloids by reversed-phase high-performance liquid chromatography on a base-deactivated stationary phase (1998)
    Springer
    Chromatographia 47 (1998), S. 21-24 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Opium alkaloids ; Papaver somniferum L.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A reversed phase HPLC method for the separation of the five major alkaloids fromPapaver somniferum L., morphine, codeine, thebaine, papaverine and noscapine, has been developed and validated. By use of a basedeactivated silica-based stationary phase excellent peak shape was achieved for each substance. The five alkaloids were quantified by internal standardization within 20 min and with good precision. The method is applicable to opium and to poppy straw.
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    On-line extraction and determination of carbofuran in raw milk by direct HPLC injection on an ISRP column (1998)
    Springer
    Chromatographia 47 (1998), S. 81-83 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Carbofuran pesticides ; On-line analysis of milk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method has been developed for extraction and determination of carbofuran in milk. The method involved direct injection of raw milk on to a human serum albumin dimethyloctyl-silica gel (HSA-C8) column and the use of 80:20 (v/v) 0.01 M phosphate buffer pH 5.5-acetonitrile as mobile phase. UV spectrophotometric detection was performed at 220 nm. Identification was based on retention time. Quantification was performed by automatic peak-area determination and was calibrated by use of an external standard.
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    High-Performance liquid chromatographic determination of dibromomannitol in plasma (1998)
    Springer
    Chromatographia 48 (1998), S. 17-19 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Dibromomannitol in plasma ; Pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Myelobromol 1,6-dibromo-1,6-dideoxy-D-mannitol (dibromomannitol, DBM) is a bifunctional alkylating agent that has been in clinical use since 1963. It is currently included at high dose in preconditioning regimen for bone marrow transplantation (BMT) and is a main-stay of treatment for polycythaemia vera. A high-performance liquid chromatographic method was developed for the determination of DBM in the plasma. The basis of the assay is a derivatization with sodium-diethyldithiocarbamate at 42°C in the presence of 1-bromo-1-deoxy-3,6-anhydro-galactitol as internal standard (IS). The analysis was carried out on a 250×4mm Hypersil 5 CPS column equipped with a 20×4 mm Hypersil 10 CPS precolumn. The eluent consisted of heptane:isopropyl-alcohol: glacial acetic acid=600:76:80 w/w. The flow rate was 1.2 mL min−1. UV detection was performed at 254 nm. The calibration graph was linear in the concentration range of 2.5–260 μM of DBM in plasma. The limit of detection was 1.0 μM. The precision and accuracy of the method was between the good laboratory practice (GLP) required limits.
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    Monitoring of biologically active amines in cereals and cereal based food products by HPLC (1998)
    Springer
    Chromatographia 48 (1998), S. 37-42 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Biologically active amines ; Polyamines ; Cereal and Cereal products
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Biologically active amines (putreanine sulphate, N-acetyl putrescine, putrescine, cadaverine, histamine, agmatine, N-acetyl spermidine, spermidine, spermine) were separated and quantified in cereal flour and cereal products by a liquid chromatographic method. The method consists of the separation of ion pairs formed between biologically active amines and octanesulphonic acid on a reversed-phase column, postcolumn derivatization with o-phtalaldehyde-2-mercapthoethanol and spectrofluorometric detection. Results of the reliability study were satisfactory. The method was linear for each amine at 1–10 mg L−1. Putrescine and spermidine were the only amines always detected in cereal flour and cereal products, ranging from 2.45 to 47.83 mg kg−1 for putrescine and 3.27 to 37.14 mg kg−1 for spermidine. The most important differences among types of samples were found in polyamine derivatives.
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    Comparative study on determination of fumagillin in fish by normal and reversed phase chromatography (1998)
    Springer
    Chromatographia 48 (1998), S. 48-52 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Normal- and reversed-phase LC ; Fumagillin in fish samples
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Fumagillin is an antibiotic agent mostly used in the veterinary profession. A normal-phase liquid chromatographic method was developed for the determination of this drug in fish matrices. A hexane-dichloromethanedioxan-2-PrOH-acetic acid (43:43:9:5:0.1 v/v %) eluent was used on a Perkin Elmer silica gel column. For validation of the process a reversed-phase HPLC method was also developed (eluent: acetonitrile-water-bicyclohyxylamine 70:30:0.05 v/v %, with Spherisorb ODS, as stationary phase). Recovery is about 100% and the limit of detection is 5 ng g−1 for meat samples.
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    HPLC separation of hydrogenated derivatives of buckminsterfullerene (1998)
    Springer
    Chromatographia 48 (1998), S. 59-64 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Buckminsterfullerene ; Hydrogenation ; Separation technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The effect of composition and flow rate of the mobile phase on the HPLC separation of hydrogenated buckminsterfullerene (C60Hn n=2–38) was investigated on BuckySep column. Toluene was used as the basic solvent and hexane, heptane, cyclohexane, THF, acetonitrile, acetone, ethanol and 2-propanol as co-solvents. The fraction of co-solvents was varied 10–80%, and the flow rate 1–0.1 mL min−1. Toluene-acetonitrile 65∶35 and toluene-acetone 50∶50 provided the best separation. Under the best conditions complete separation of C60H2 and almost complete separation of the four most abundant isomers of C60H4 were achieved. Separation of derivatives with higher hydrogen content was very poor.
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    The preparative chromatographic enantioseparation of a racemic morphanthridine analog on a chiral stationary phase (1998)
    Springer
    Chromatographia 47 (1998), S. 440-442 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Preparative scale separations ; Chiral stationary phase ; Enantiomer separation ; Morphanthridine analog
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The preparative chromatographic enantioseparation of a chiral morphoanthridine analog has been performed on an analytical column using amylose-tris(3,5-dimethylphenylcarbamate) as chiral stationary phase. The racemate (100 mg) was resolved to baseline within 15 min. This paper describes the development of the method, estimation of the capacity of the chiral stationary phase and discussed the potential of the chromatography if performed under preparative conditions. From the results and calculations presented it seems likely that the resolution of 70 tons year−1 could easily be achieved on 30 kg of stationary phase with a mobile-phase consumption of only 720 L day−1.
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    URL: http://dx.doi.org/10.1007/BF02466476
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    An improved extraction of marrubiim fromMarrubium vulgare (1998)
    Springer
    Chromatographia 47 (1998), S. 449-450 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chitin stationary phase ; Marrubiin ; Analgesic activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Marrubiin is the main active compound isolated fromM. vulgare, a medicinal plant used in folk medicine to cure several diseases. The present study shows that chitin, an abundant natural polymer, may be successfully in chromatography column to separate marrubiin from complex mixtures. The experimental procedure described here represents an efficient and rapid method to obtain such compound in high yield.
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    URL: http://dx.doi.org/10.1007/BF02466478
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    Applications of molecularly imprinted materials as selective adsorbents: Emphasis on enzymatic equilibrium shifting and library screening (1998)
    Springer
    Chromatographia 47 (1998), S. 465-469 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Affinity chromatography ; Molecular imprinting ; Molecular recognition ; Combinatorial libraries
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Molecular imprinting is an attractive method for producing highly selective adsorbents, and several new and potentially useful applications based on molecularly imprinted polymers (MIPs) have been described in recent years. In this article, we highlight some of the areas where these materials have found application, and also describe some new fields of application where the selectivities of imprinted materials can be gainfully employed, for example as binding matrices in the screening of combinatorial libraries, and as auxiliary agents in enzymatic syntheses.
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    URL: http://dx.doi.org/10.1007/BF02466482
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    On-line monitoring of monosaccharides and ethanol during a fermentation by microdialysis sampling, liquid chromatography and two amperometric biosensors (1998)
    Springer
    Chromatographia 47 (1998), S. 501-508 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Fermentation ; Microdialysis sampling ; Monosaccharides and ethanol ; On-line monitoring ; Biosensors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Two amperometric biosensors were used as detection units in liquid chromatography for on-line monitoring of the production of fuel ethanol during a fermentation. Sampling was performed with a microdialysis probe, and the dialysate was introduced into a liquid chromatographic system providing separation of the substrates and the product: three monosaccharides and ethanol. The analytes were detected by two carbon paste electrodes based on pyranose oxidase and alcohol oxidase, respectively, co-immobilised with horseradish peroxidase, operating in parallel at −50 mVvs. Ag/AgCl. The measured linear ranges of the biosensors by direct injection into the LC system were for glucose 0.3–2.5 g L−1, xylose 0.5–6.7 g L−1, galactose 0.5–6.7 g L−1, and ethanol 1.6–11.7 g L−1, respectively. Injection of standard solutions were required to monitor the stability of the biosensors. Due to the strict selectivity of the biosensors, no interference from other compounds in the broth was encountered from other compounds in the broth was encountered in the quantification. The fermentation process was monitored for 16 h. The on-line results were compared with off-line measurements.
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    URL: http://dx.doi.org/10.1007/BF02467486
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    Determination of cisapride in human plasma by high-performance liquid chromatography (1998)
    Springer
    Chromatographia 47 (1998), S. 537-541 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Cisapride in plasma ; Pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An HPLC method has been developed for the quantification of cisapride in plasma for pharmacokinetic studies. Clebopride was used as internal standard. Plasma samples were extracted at alkaline pH withtert-butyl methyl ether. The organic phase was then extracted with sulphuric acid to eliminate endogenous interferences, and cisapride and the internal standard were then extracted at alkaline pH intotert-butyl methyl ether. After evaporation oftert-butyl methyl ether, the residue was analysed by HPLC. Chromatography was performed at 20°C on a 250mm×4mm i.d. reversed-phase column selective for basic compounds. The isocratic mobile phase was 48∶52 (v/v) acetonitrile-water containing 0.05 M potassium dihydrogen phosphate and 0.04 M triethylamine, adjusted to pH 5.5; the flow rate was 1 mL min−1. Cisapride and the internal standard were detected by ultraviolet monitoring at 276 nm. The calibration graph was linear for quantities of cisapride from 1 to 200 ng mL−1. Intra- and inter-day precision (CV) did not exceed 13.98%. The limit of quantitation (LOQ) was 0.68 ng mL−1 for human plasma. The applicability of the method has been demonstrated in a pharmacokinetic study of normal volunteers who received 10 mg cisapride orally.
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    URL: http://dx.doi.org/10.1007/BF02467491
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    Enantiomeric separation of four methylenedioxylated amphetamines on β-cyclodextrin chiral stationary phases (1998)
    Springer
    Chromatographia 47 (1998), S. 285-290 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Enantiomeric separation ; β-Cyclodextrins ; Methylenedioxylated amphetamines ; Ecstasy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Native and derivatized β-cyclodextrins such as chiral stationary phases (CSP) were used for the simultaneous enantiomeric separation of four methylenedioxylated amphetamines (MDA, MDMA, MDEA and MBDB) by liquid chromatography. Fluorimetric detection was used in order to enhance sensitivity and selectivity. The mobile phase was, optimised by studying the influence of pH, triethylamine concentration, organic solvent type, column temperature and flow rate of the mobile phase. This method was validated by determining linearity, precision, accuracy, limits of detection and quantification, and was applied to the stereoselective analysis of illicit tablets (23 samples) and of human whole blood samples (spiked samples and two post-mortem cases). Whereas no significant deviation from a racemic ratio was observed in the tablets contents, the analysis of blood samples showed an enantioselective metabolism of MDMA.
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    URL: http://dx.doi.org/10.1007/BF02466533
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    Aminopropyl-silica as an advantageous alternative to nonpolar sorbents for continuous cleanup/preconcentration of vitamin D3 metabolites (1998)
    Springer
    Chromatographia 47 (1998), S. 367-372 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Aminopropyl-silica sorbent ; Continuous cleanup/preconcentration ; Hydroxyvitamin D3 metabolites ; Flow injection analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new procedure for continuous cleanup and concentration of hydroxyvitamin D3 metabolites prior to their separation by HPLC and UV-detection is reported. The process is based on the use of aminopropyl-silica as solid-phase sorbent as an alternative to the use of nonpolar sorbents. The improvement thus achieved has been tested by comparing the results with those obtained using octadecyl-C18 as non-polar sorbent. The comparison has been based on the calibration graphs (linear range, detection and quantitation limits), precision and multiple standard addition method.
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    URL: http://dx.doi.org/10.1007/BF02466466
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    Simultaneous determination of 3,4-dihydroxymandelic acid, 4-hydroxy-3-methoxymandelic acid, 3,4-dihydroxyphenylglycol, 4-hydroxy-3-methoxyphenylglycol, and their precursors, in human urine by HPLC with electrochemical detection (1998)
    Springer
    Chromatographia 47 (1998), S. 396-400 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Coulometric detection ; Mandelic acids ; Phenylglycols ; Urine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method has been developed for the quantification of urinary 3,4-dihydroxymandelic acid (DOMA), 4-hydroxy-3-methoxymandelic acid (VMA), 3,4-dihydroxyphenylglycol (DHPG), and 4-hydroxy-3-methoxyphenyglycol (MHPG). Separation and determination of these compounds in biological samples was previously thought to be very difficult. In this work the separation has been achieved by reversed-phase high-performance liquid chromatography with step-wise gradient elution with three mobile phases. The conditions for coulometric detection have been optimized for effective determination of these compounds. In analysis of a sample of human urine, after a simple deproteinization proceudre, DOMA, VMA, DHPG, and MHPG were separated from interferences and quantified successfully; the average levels of these compounds in six different samples were 33.87±1.03, 1202±41.3, 31.3±1.92, and 80.6±2.15 μg (24 h)−1, respectively. Their precursors E, MN, DOPA, DA, NE, DOPAC, HVA, 3MT, and NMN, and the indolamine 5HT and its metabolite 5HIAA (a list of abbreviations is given at the end of the paper) can also be determined simultaneously in the same chromatographic run. The overlapping peak of DHPG was resolved by deconvolution.
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    URL: http://dx.doi.org/10.1007/BF02466470
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    Optimization of solvent selectivity for the chromatographic separation of fat-soluble vitamins using a mixture-design statistical technique (1998)
    Springer
    Chromatographia 47 (1998), S. 401-412 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Optimization ; Mixture design ; Special cubic polynomial model ; Pareto-optimality ; Overlapping resolution mapping (ORM)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A systematic approach, using a mixture-design statistical technique, has been developed for selecting the optimum mobile phase for the separation of fat-soluble vitamins in reversed-phase high-performance liquid chromatography. A quaternary mixture of methanol, acetonitrile, tetrahydrofuran and water was used as mobile phase. Retention time and peak width were recorded in ten runs augmented with five replicates and the data were subsequently fitted to special cubic polynomial models. The resulting mathematical equations enabled prediction of resolution over the entire parameter space. Contour plots of minimum effective resolution and maximum retention time as a function of mobile phase composition are presented and discussed. Visual inspection of these plots provides an overview of the quality of the separation and the analysis time required for each possible mobile-phase composition with n the parameter space. It is demonstrated that the methodology followed was an important tool which enabled the taking of informed decisions necessary for selection of the optimum mobile phase for a chromatographic separation. A combination ofR S minimum andt R maximum as optimization criteria in a multicriteria decision-making plot using pareto-optimality concept is discussed. This combination enabled visual demonstration of the compromise between separation quality and the economics of analysis time. Our methodology has been compared with the common used technique of ‘overlapping resolution mapping’.
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    URL: http://dx.doi.org/10.1007/BF02466471
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    Predicting the selectivity of imprinted polymers (1998)
    Springer
    Chromatographia 47 (1998), S. 457-464 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Imprinted polymer ; Non-covalent imprinting ; Selectivity and capacity ; Association constant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Imprinted polymers as stationary phases for HPLC separations have been the subject of extensive investigations in recent years. In order to aid the rational design of synthetic protocols for the preparation of imprinted polymers, a series of calculations were made to assess the equilibrium concentration of templatemonomer complexes as a function of association constant (K) for the functional groups involved in the interactions and initial concentrations of reactants. This data was then used to predict the selectivity of polymers prepared under different reaction conditions and the model was tested using an experimentally determined value ofK and separation factors taken from the literature.
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    URL: http://dx.doi.org/10.1007/BF02466481
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    Chiral discrimination ofN-(dansyl)-dl-amino acids on human serum albumin stationary phase: Effect of a mobile phase modifier (1998)
    Springer
    Chromatographia 48 (1998), S. 431-435 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; N-(dansyl)-dl-amino acids ; Human serum albumin ; Chiral discrimination ; Optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The effect of perchlorate anion as mobile phase modifier on the separation factor, α, forN-(dansyl)-dl-norvaline andN-(dansyl)-dl-tryptophan on a human serum albumin (HSA) column was studied by varying the concentration,c, of the chaotropic agent and the column temperatureT. Gibbs-Helmholtz parameters Δ(ΔH) and Δ(ΔS) between thed andl enantiomers were determined from linear van't Hoff plots of lnα against 1/T. Thermodynamic results indicated that the enhancement of the separation factor observed asc was increased was enthalpically controlled owing to stereoselective H-bonding interactions. Such behavior was used to optimize the chromatographic conditions for separation ofN-(dansyl)-amino acids on HSA.
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    URL: http://dx.doi.org/10.1007/BF02467716
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    Determination of two metabolites of albendazole, albendazole-sulfoxide and albendazole-sulfone in cow's milk using an HPLC method —A systematic approach to optimise extraction conditions (1998)
    Springer
    Chromatographia 48 (1998), S. 777-784 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Solid phase extraction ; Sample treatment optimisation ; Taguchi method ; Albendazole metabolites ; Milk samples
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Reversed phase HPLC methods for the determination of two metabolites of albendazole in cow's milk are described. Albendazole is an anthelmintic agent used both in veterinary and human practice. Its main metabolites are albendazole-sulfoxide and albendazole-sulfone. The separation of the two metabolites was performed on a μ-Bondapak C-18 column using an acetonitrile/methanol/phosphate buffer as mobile phase, with detection at 290 nm. For the sample preparation of the milk samples we used solid phase extraction. A new sample treatment optimisation procedure is also presented for the sample preparation method. Since sample preparation is a critical step in the analysis of residues in biological samples, the second part of our publication describes an optimisation using Taguchi's methodology that increased recovery, accuracy and reliability. After optimisation of the sample preparation, the limit of detection was 10 ng mL−1 milk and the recovery was 70–80% in the concentration range of 30–1000 ng mL−1 milk for both metabolities.
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    Development and validation of stability indicating high-performance liquid chromatographic assays for ketotifen in aqueous and silicon oil formulations (1998)
    Springer
    Chromatographia 48 (1998), S. 797-802 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ketotifen analysis ; Stability indicating analysis ; Aqueous and oil-based formulations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple and specific high-performance liquid chromatographic (HPLC) method for the analysis of ketotifen in aqueous solutions and silicon oil suspensions is described. The HPLC system is based on a reversed phase μBondapak C18 (30×0.39 cm) column with a mobile phase of phosphate buffer (0.001 M, pH 7.4):methanol: acetonitrile: trimethylamine (29.8:45:25:0.2, by volume) at a flow-rate of 1 mL min−1. The eluent was monitored by UV absorption at 299 nm. Silicon oil-based samples were extracted with HCl (0.05 M) using imipramine as internal standard. The recovery of ketotifen and imipramine was greater than 80%. The calibration curves for both assays were linear over the ranges examined, yielding correlation coefficients greater than 0.997. The assay was shown to be stability indicating by subjecting solutions of ketotifen in phosphate buffer to heat, oxidative stress and irradiation with ultraviolet light (254 and 369 nm)for up to 8 h. The methodology was also shown to be applicable for the analysis of ketotifen in simple aqueous based formulations, in suspension in silicon oil and for the analysis of samples derived fromin vitro skin transfer experiments.
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    URL: http://dx.doi.org/10.1007/BF02467650
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    An improved method for assay of vitamin C in fish feed and tissues (1998)
    Springer
    Chromatographia 48 (1998), S. 43-47 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Vitamin C analysis ; Ascorbate-2-phosphate and sulphate esters ; Enzyme shifting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method was devised to assay four forms of vitamin C: L-ascorbic acid (AA), dehydroascorbic acid (DHA), ascorbate-2-mono- and polyphosphate (AMP, APP), as well as ascorbate-2-monosulphate (AMS), in sample series of different fish tissues and feed. Direct and indirect detection were combined. Sample extractions were carried out with 0.2 mol L−1 sodium acetate buffer (pH 4.8) and extracts were deproteinized after different chemical or enzymatic reactions, with perchloric acid. The DHA was reduced to AA with dithioerythritol (DTE). Ascorbate oxidase enzyme was used for the detection of background and an acidic phosphatase enzyme for the hydrolysis of different phosphate esters. Ascorbate-2-sulphate was detected directly with help of coinjection of the compound. Chromatographic analysis was carried out with a single column isocratic reverse phase method. The mobile phase was an aqueous buffer of 0.04 M sodium-acetate, 0.05 mM EDTA, 0.5 mM tetrabutylammonium dihydrogen phosphate (TBA) adjusted to pH 3.76 with 85% H3PO4 and with 24 mL methanol added to 1000 mL. C-18 columns were used with 0.6 mL min−1 flow rate at 23°C. The vitamin C forms were detected by UV absorption at 250 nm. The determination limit was 1.0–5.0 μg g−1 in AA equivalent. The standard deviations were between 1–6% and depended on the concentrations of vitamin C forms and tissues. Recoveries were between 90–96% in samples.
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    URL: http://dx.doi.org/10.1007/BF02467514
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    Liquid chromatography of polymer mixtures by a combination of exclusion and full adsorption mechanisms. Three- and four-component polymer blends (1998)
    Springer
    Chromatographia 48 (1998), S. 65-70 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Multicomponent mixtures ; Separation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Coupling of full adsorption-desorption and size-exclusion chromatography (FAD-SEC) has been applied to the separation and molecular characterization of three- and four-component polymer blends. The method is based on the full adsorption of alln orn−1 components of the polymer blend in a specially designed FAD minicolumn. By appropriate eluent switching the adsorbed polymers are desorbed stepwise from the FAD minicolumn into an on-line SEC column for molecular characterization. It is shown that the desorption isotherms of particular blend components give valuable information about the appropriate displacer composition. The exact position of the desorption isotherms depends, however, both on the amount of polymer adsorbed and in the presence of other, chemically different, polymers within FAD column. The nature and composition of the displacer must, therfore, be adjusted if the intervals between the desorption of particular blend components are to be large enough to prevent displacement overlap.
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    URL: http://dx.doi.org/10.1007/BF02467518
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    The RP-HPLC analysis of anthocyanins (1998)
    Springer
    Chromatographia 48 (1998), S. 360-364 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Acylated anthocyanins ; Rudbeckia hirta L. ; In vitro cultures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Conditions were determined for the separation of a complex set of anthocyanins (free aglycones, mono- and multiglycosides and esterified forms) by HPLC. The optimised gradient elution method was then used to carry out qualitative and quantitative analysis of anthocyanin compounds present in the callus tissue ofRudbeckia hirta L. and the tubular flowers of the soil-based plant. The summary content of anthocyanin pigments and the content of the main pigment was identified in the analysed biomass. The method developed is useful for the purposes of monitoring the process of biosynthesis of anthocyanins in tissues obtained through in vitro cultures. The advantages of the method for anthocyanins and its application to other anthocyanin-rich materials are also discussed.
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    URL: http://dx.doi.org/10.1007/BF02467704
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    Effects of amine additives on the resolution of antipsychotic and antidepressant drugs on a cyanoalkyl HPLC column (1998)
    Springer
    Chromatographia 48 (1998), S. 770-776 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Basic drug compounds ; Amino additives ; Cyanoalkyl columns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of basic antidepressant and antipsychotic drugs on a cyanoalkyl-bonded silica column has been studied to determine the effects on peak retention, symmetry, efficiency, and resolution of six different amine mobile-phase additives. The amines—ammonia,n-butylamine, triethylamine,N,N-diisopropylethylamine,N,N-dimethylbutylamine andN,N-dimethyloctylamine—were, except forN,N-diisopropylethylamine, chosen because of their widespread use for improvement of peak symmetry in chromatographic methods;N,N-diisopropylethylamine was included as an example of a sterically hindered amine to see if the stereochemistry around the nitrogen atom is an important consideration in the selection of an additive. This study shows that a gain in symmetry and efficiency is accompanied by loss of resolution. The results obtained also indicate that one type of amine additive should be used when symmetry and efficiency are most important and another when resolution is paramount.
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    Extraction and liquid-chromatographic determination of amphotericin B in oil-water lecithin-based microemulsions (1998)
    Springer
    Chromatographia 48 (1998), S. 803-806 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Amphotericin B ; Oil-water lecithin-based microemulsions ; Extraction of drug from microemulsion ; Reversed-phase HPLC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method employing extraction then reproducible reversed-phase high-performance liquid chromatography (RPHPLC) with monitoring of the drug by absorbance at 405 nm has been developed and validated for the determination of amphotericin B in oil-water lecithin-based microemulsions. The precision and accuracy of the method are excellent (SD 2.4% and 4.2%, respectively). The established linearity range was 10–60 μg mL−1 (r 2=0.9967). The recovery of amphotericin B from spiked placebo was 〉90% over the linear range. The extraction procedure was simple and the HPLC conditions were able to separate the drug from its degradation products and excipients. The method has been used successfully for determining the amphotericin B content of microemulsions and for evaluating the chemical stability of amphotericin B-loaded microemulsions.
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    URL: http://dx.doi.org/10.1007/BF02467651
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    Studies on shape selectivity of RP C18-columns (1998)
    Springer
    Chromatographia 48 (1998), S. 183-189 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polymeric phases ; Shape selectivity ; PAH selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Stationary phases with octadecyl groups have been prepared with different carbon content without and in the presence of water and characterized for their selectivity for the shape of various polyaromatic hydrocarbons. It is shown that both a high hydrocarbon content and a good accessibility of the bonded groups within the pores is required to achieve shape recognition for PAH. High carbon content alone is not sufficient. The two tests for shape selectivity proposed by Sander and Wise as well as by Tanaka are compared. In most cases the results are similar: A low selectivity with the Sander and Wise test (α TBN/BaP〈1) corresponds to a high value with the Tanaka test (α TRI/o-TER〉3). However, not in all cases the tests give corresponding answers. Further studies on molecular recognition are required.
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    URL: http://dx.doi.org/10.1007/BF02467669
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