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  • Column liquid chromatography  (1,216)
  • Allgemeine Geographie
  • E62
  • Springer  (1,229)
  • Wiley  (1)
  • Amsterdam and Rotterdam: Tinbergen Institute
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  • 1
    Electronic Resource
    Electronic Resource
    Relative consumption, economic growth, and taxation (2000)
    Springer
    Journal of economics 72 (2000), S. 241-262 
    Details
    ISSN: 1617-7134
    Keywords: social status ; relative consumption ; economic growth ; D62 ; D91 ; E21 ; E62
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract This paper studies the influence of consumption externalities in the Ramsey model. In contrast to the recent literature, a quite general specification of preferences is used and the concept of the effective intertemporal elasticity of substitution is introduced. We give conditions for the observational equivalence between economies with consumption externalities and externality-free economies. An additional key result is that there exist several types of instantaneous utility functions in which the decentralized solution coincides with the socially planned one in spite of the presence of consumption externalities. The conditions for optimal taxation are also derived.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01231266
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  • 2
    Electronic Resource
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    Global indeterminacy in an endogenous-growth model with public capital (2000)
    Springer
    Journal of economics 71 (2000), S. 255-280 
    Details
    ISSN: 1617-7134
    Keywords: endogenous growth ; public capital ; indeterminacy ; limit cycles ; E62 ; H54 ; O41
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract This paper studies the patterns of growth in an endogenous-growth model where the labor supply is endogenous and sustained growth arises because the services derived from public capital increase the economic productivity. It is assumed that these services are congested by the number of households in the economy but they are not congested by the units of time that each household devotes to work. With this assumption, the dynamic equilibrium exhibits multiple balanced-growth paths, local and global indeterminacy, and limit cycles under some plausible fiscal policies. Our analysis points out that a large lump-sum tax is a necessary condition to obtain this complex equilibrium dynamic behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01228743
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  • 3
    Electronic Resource
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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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467760
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  • 4
    Electronic Resource
    Electronic Resource
    Unexpected behavior of digoxin at elevated temperatures in reversed-phase liquid chromatography (1999)
    Springer
    Chromatographia 49 (1999), S. 306-308 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467561
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  • 5
    Electronic Resource
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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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467185
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  • 6
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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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467189
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  • 7
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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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467194
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  • 8
    Electronic Resource
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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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02466900
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  • 9
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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 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467609
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  • 10
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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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02468972
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  • 11
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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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02466905
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  • 12
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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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02466906
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  • 13
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    Determination of flupoxam residues in soil by high performance liquid chromatography (1999)
    Springer
    Chromatographia 49 (1999), S. 535-538 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467754
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  • 14
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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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    URL: http://dx.doi.org/10.1007/BF02467567
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  • 15
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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 
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    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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    URL: http://dx.doi.org/10.1007/BF02467607
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  • 16
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    Comparison of octadecyl bonded titania phases (1999)
    Springer
    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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    URL: http://dx.doi.org/10.1007/BF02467618
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  • 17
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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 
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    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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    URL: http://dx.doi.org/10.1007/BF02466915
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  • 18
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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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  • 19
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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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    URL: http://dx.doi.org/10.1007/BF02467180
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  • 20
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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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    URL: http://dx.doi.org/10.1007/BF02467181
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  • 21
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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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    URL: http://dx.doi.org/10.1007/BF02467186
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  • 22
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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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    URL: http://dx.doi.org/10.1007/BF02467188
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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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    URL: http://dx.doi.org/10.1007/BF02467191
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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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    URL: http://dx.doi.org/10.1007/BF02467195
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    Hydrolysis of microcystins and nodularin by microwave radiation (1999)
    Springer
    Chromatographia 49 (1999), S. 671-677 
    Details
    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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    URL: http://dx.doi.org/10.1007/BF02466910
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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 
    Details
    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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    URL: http://dx.doi.org/10.1007/BF02466914
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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 
    Details
    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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    URL: http://dx.doi.org/10.1007/BF02467550
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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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    URL: http://dx.doi.org/10.1007/BF02467557
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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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    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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    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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    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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    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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    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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    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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    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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    Analysis of doxorubicin in cell culture media and human plasma using solid phase extraction and HPLC (1999)
    Springer
    Chromatographia 49 (1999), S. 557-561 
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    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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    Options and sunspots in a simple monetary economy (1998)
    Springer
    Economic theory 11 (1998), S. 295-315 
    Details
    ISSN: 1432-0479
    Keywords: JEL Classification Numbers: D52 ; D84 ; E62 ; G10.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Summary. We study sunspot immunity in a dynamic monetary economy in which consumers are allowed to trade put and call option contracts on the general price level. We define the concept of strong sunspot immunity to characterize economies that have no sunspot equilibria regardless of the number of extrinsic states and their probabilities of occurrence. We show that a small number of option contracts can make an economy strongly sunspot immune. In addition, we demonstrate how asset re-trading opportunities, and the associated capital gains and losses, reduce the number of options needed for this result to obtain.
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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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    Interlaboratory study of analysis of phenoxymethylpenicillin by liquid chromatography (1998)
    Springer
    Chromatographia 47 (1998), S. 152-156 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Phenoxymethylpenicillin ; Collaborative study
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A liquid chromatography method for analysis of phenoxymethylpenicillin has been examined in a collaborative study involving 6 laboratories. The method comprised an isocratic part, which is used in the assay. When the isocratic part is combined with gradient elution, the method is suitable for purity control. Five samples of phenoxymethylpenicillin (potassium salts and acid) were analysed. The main component, the most important side product 4-hydroxyphenoxymethyl-penicillin and other impurities were determined. An analysis of variance proved the absence of consistent laboratory bias. Laboratory-sample interaction was not significant. Estimates of the repeatability and reproducibility of the method, expressed as standard deviations (SD) of the result of the determination of phenoxymethylpenicillin, were 0.50 and 0.63 respectively.
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    Bile acids as stationary phase in liquid chromatography (1998)
    Springer
    Chromatographia 47 (1998), S. 183-188 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Bile acid aggregates as stationary phase ; Enantiomeric separation ; 1,1′-Binaphthyl-2,2′-diyl-hydrogenphosphate enantiomers ; Dansyl amino acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Bile acids chemically bonded onto aminopropylsilica have been employed as stationary phases in liquid chromatography. Bile acid aggregates were dynamically formed around molecules chemically anchored on the supports when the eluent contained bile salts. The bile salt aggregates achieved the separation of 1,1′-binaphthyl-2,2′-diyl-hydrogenphosphate enantiomers and dansyl amino acids.
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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 
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    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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    Retention study on silica gel in high-temperature liquid chromatography (HTLC) (1998)
    Springer
    Chromatographia 47 (1998), S. 278-284 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; High-temperature columns ; Retention behavior ; Column equilibration ; Bilayer formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Retention volumes (V N) of different kinds of test compound have been measured on silica gel as a function of column temperature (T) in the range 20 to 210°C.n-Heptane and mixtures ofn-heptane and polar modifiers were used as mobile phases. With nC7 and nC7-1,4-dioxane mixtures, there was a good linear relationship between InV N and 1/T for column temperatures above 100 °C. When more polar modifiers such as butanol, ethanol and acetic acid were used, ‘N’-shaped curves were obtained for the plots of InV N against 1/T. Possible explanations of this retention behavior have been proposed on the basis of related studies and common physical chemistry relationships. Column equilibration time after alteration of water content or column temperature is greatly reduced at elevated temperatures. This will benefit the application of LSC on silica gel.
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  • 47
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    Ligand-exchange chromatographic separation of DL-amino acids on aminopropylsilica-bonded chirals-triazines (1998)
    Springer
    Chromatographia 47 (1998), S. 637-642 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ligand-exchange chromatography ; Chiral stationary phases ; Enantiomer separation ; Amino acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Chiral stationary phases (CSPs) were synthesized by reaction of aminopropylsilica (APS) with chiral monochloro-s-triazines (MCTs). MCTs were obtained by reaction of 2,4,6-trichloro-s-triazine (cyanuric chloride) with one equivalent of methanol and, subsequently, with one equivalent of L-prolinetert butyl ester (H-Pro-OtBu) orN-tert butyloxycarbonyl-L-lysinetert butyl ester (Boc-Lys-OtBu). End-capping of unreacted amino groups of APS with acetic anhydride, followed by trifluoroacetolytic cleavage of the protecting groups of amino acids (AAs), afforded two chiral stationary phases bearing either L-proline (CSP-3) or L-lysine (CSP-4) as chiral selector. Using ligand-exchange chromatography matography with addition of Cu2+ to the mobile phase, enantiomers of free DL-AAs and a fewN-(2,4-dinitrophenyl)-DL-AAs were separated on CSP-3, whereasN-(dansyl)-DL-AAs were separated on CSP-4.
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    Determination of glucuronides of molecules of toxicological interest by liquid chromatography negative-ion mass spectrometry with atmospheric pressure chemical ionization (1998)
    Springer
    Chromatographia 47 (1998), S. 659-666 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Atmopheric Pressure Chemical Ionization (APCI) mass ; spectrometry ; Glucuronide-conjugates ; Toxicological compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new chromatographic method for the direct determination of metabolites (glucuronide-conjugates) of molecules of toxicological relevance in biological media with the minimum sample pre-treatment has been developed. A high performance liquid chromatographyatmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) system was used for this purpose. The separation of four glucuronides Aminophenylglucuronide (APhG), Phenylglucuronide (PhG),p-Nitrophenylglucuronide (NPhG) and α-Naphthylglucuronide (NG) was obtained under ion-suppressed reversed-phase chromatography conditions, by using high-speed (3 cm, 3 μm) columns and formic acid (2 mM) as the acid modifier in the mobile phase. Different C-18 stationary phases (partially endcapped and non-endcapped) were evaluated in order to obtain retention for these very polar, water soluble molecules. The ionization of the analytes was obtained in negativeion (NI) mode. Detection limits were in the range 1–5 mg L−1 and calibration curves were linear over two order of magnitude. Intra-day and inter-day precision were in the range 2.9–10.6% for all the compounds. The method was successfully applied for the determination of PhG in a urine sample of a European Quality Assurance Programme for Organic Solvent Metabolites.
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    Direct solid-phase microextraction combined with gas and liquid chromatography for the determination of lidocaine in human urine (1998)
    Springer
    Chromatographia 47 (1998), S. 678-684 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Column liquid chromatography ; Solid-phase microextraction ; Local anaesthetic lidocaine ; Optimisation of extraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Solid-phase microextraction (SPME) has been combined with gas chromatography (GC) and liquid chromatography (LC) for the determination of lidocaine in human urine. A polydimethylsiloxane (PDMS) coated fibre was directly immersed into buffered urine. Extraction conditions such as time, pH, ionic strength, temperature, and agitation were optimised. The extracted lidocaine was thermally desorbed in a split/splitless injector for analysis with a GC-FID system or desorbed with liquid in a specially designed SPME-LC interface for analysis with an LC-UV system. After optimisation the method developed was evaluated and validated. Extraction yields of 22% were obtained in about 45 min. The reproducibility of the method is 〈5% (relative standard deviation). For five-times diluted urine, linear ranges were found from 5–1000 and 25–1000 ng·mL−1 for SPME-GC and SPME-LC, with detection limits of 5 ng·mL−1 for SPME-GC and 25 ng·mL−1 for SPME-LC. SPME can be used as a simple sample pretreatment method for the determination of lidocaine in urine by GC and LC.
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    Porous copolymer of the methacrylic ester of dihydroxydiphenylmethane diglycidyl ether and divinylbenzene as an HPLC packing (1998)
    Springer
    Chromatographia 47 (1998), S. 509-514 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Porous copolymers with hydroxyl groups ; Chemical modification of phases ; Selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Dimethyldichlorosilane has been used to deactivate the hydroxyl groups present in the skeleton of the porous polymer formed from the methacrylic ester ofp, p′-dihydroxydiphenylmethane diglycidyl ether and divinylbenzene. The influence of chemical modification of the copolymer on its chromatographic behavior has been studied. The retention indices of five homologous series and test compounds were calculated to determine the selectivity of the packings.
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    Analysis of anka pigments by liquid chromatography with diode array detection and tandem mass spectrometry (1998)
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    Chromatographia 47 (1998), S. 529-536 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Thin layer chromatography ; Mass spectrometry detection ; Anka pigments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Anka is withMonascus sp. fermented rice, which shows a purplish red color. On rice grainsMonascus purpureus DSM 1379 synthesized four anka pigments. Through extraction of anka with n-hexane and methanol in succession and through repeated crystallizations from absolute ethanol anka pigments were crystallized into two fractions: organge anka pigments (rubropunctatin and monascorubrin) and yellow anka pigments (monascin and ankaflavin). The treatment of two organge anka pigments with aqueous ammonia solution gave red nitrogen analogues (rubropunctatamine and monascorubramine). The above six pigments were separated into each pigment by two dimensional thin layer chromatography (TLC) or high performance liquid chromatography (HPLC). HPLC-atmospheric pressure chemical ionization-tandem mass spectrometry (HPLC-APCI-MS-MS) and direct probe mass spectrometry (MS) were used to identify these pigments. HPLC-diode array detector (HPLC-DAD) was used to determine UV-VIS spectra of pigments. Pigments were analyzed with HPLC under the following conditions: C18 column, acetonitrile/water (80∶20, v/v), 0.5 mL min−1, 233 nm.
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    Determination of nalbuphine hydrochloride, methylparaben, and propylparaben in nalbuphine hydrochloride injection by high performance liquid chromatography (1998)
    Springer
    Chromatographia 47 (1998), S. 515-522 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; 4,5-Epoxymorphinan ; Nalbuphine hydrochloride injection ; Stability assays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A stability-indicating liquid chromatographic method has been developed for the determination of nalbuphine hydrochloride, methylparaben, and propylparaben in nalbuphine hydrochloride injection. Reversed-phase chromatography was carried out using a mobile phase containing 0.05 % trifuoroacetic acid, acetonitrile, and tetrahydrofuran. Quantitation was achieved with UV detection at 280 nm. Validation data for linearity, accuracy, precision, specificity, and robustness are presented. The chromatographic system resolves nalbuphine from synthetic impurities and degradation products.
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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 
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    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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    Liquid chromatographic analysis of non-volatile strawberry compounds (1998)
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    Chromatographia 47 (1998), S. 197-202 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Non-volatile strawberry compounds ; Multivariate analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A procedure is presented for simultaneous extraction of organic acids, vitamin C and sugars from strawberries and analysis by reversed-phase (RP) HPLC and cationexchange (calcium form) chromatography. Recoveries from strawberries spiked at different levels ranged from 96 to 103 % for carbohydrates, 92 to 112 % for organic acids, and 84 % for vitamin C; the repeatability of the method evaluated as the relative standard deviation in the optimum range was 〈5 % for sugars and 7.5 % for organic acids and vitamin C. Multivariate analysis techniques, such as Bayes and SIMCA analyses, have enabled correct classification of the strawberries tested but we were unable to establish adequate models for typifying them according to their geographic origin.
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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 
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    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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    The application of high performance liquid chromatography, coupled to nuclear magnetic resonance spectroscopy and mass spectrometry (HPLC-NMR-MS), to the characterisation of ibuprofen metabolites from human urine (1998)
    Springer
    Chromatographia 47 (1998), S. 264-270 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; NMR and MS detection ; Ibuprofen metabolites ; Urine extracts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The use of HPLC-NMR-MS for the detection and identification of the metabolites of ibuprofen present in a solid phase extract of human urine is described. Gradient reversed-phase HPLC was used to separate the components present in the extract, which were then characterised by a combination of stopped-flow1H NMR and on line electrospray-MS. This approach led to the rapid identification of the known phase 1 human metabolites of ibuprofen, including hydroxy- and carboxy- metabolites, together with their respective glucuronide conjugates. In addition a probable artefact resulting from the dehydration of one of the side chainhydroxylated glucuronides was also identified.
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    Use of short columns and high flow rates for rapid gradient reversed-phase chromatography (1998)
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    Chromatographia 47 (1998), S. 291-298 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Capillary electrochromatography ; Rapid analysis ; Short columns ; Rapid gradients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Rapid analyses were performed using reversed-phase liquid chromatography with short (20–100 mm) columns swept by fast yet shallow gradients, and the results compared with those obtained with 150 mm columns and slow gradients. The resolution losses incurred with shorter columns were minimised by employing elevated flow rates, to ensure that comparable mean retention factors were experienced by individual analytes during gradients run on different columns. This conserves gradient steepness. High quality performance was obtained with turn-around times of 5–10 minutes. An overall 5-fold enhancement in the rate of information generation was obtained. The relevance of instrumental parameters and of column and packing dimensions, upon the potential for improved performance is discussed. Some implications for the rapidly developing technique of capillary electrochromatography are briefly indicated.
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    Separation of lansoprazole enantiomers in human serum by HPLC (1998)
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    Chromatographia 47 (1998), S. 171-175 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Lansoprazole ; Enantiomers ; Human serum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new and simple HPLC method is described for the separation and quantitative determination of the (+)-and (−)-enantiomers of lansoprazole. The analytes were extracted from serum as previously described for whole lansoprazole [K. Borner, Chromatographia 45, 450–452 (1997)]. The enantiomers were separated by chromatography on a CHIRAL-AGPR column which contained covalently bound acid α1-glycoprotein as chiral selector. In the pure drug the (−)/(+) ratio was 0.99:1.01. In serum of twelve human volunteers the concentration of the (−)-enantiomer was 3 to 5 times higher than that of the (+)-enantiomer. Both enantiomers differ remarkably in their pharmacokinetics.
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    Determination of eleven priority EPA phenolics at ng L−1 levels by on-line solid-phase extraction and liquid chromatography with UV and electrochemical detection (1998)
    Springer
    Chromatographia 47 (1998), S. 176-182 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Electrochemical detection ; Phenolics in water ; On-line preconcentration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The eleven priority, EPA phenolic pollutants were determined by liquid chromatography followed by two detectors in series; UV and electrochemical. Three different adsorbents, Envi-Carb (a carbon black) and two functionalized polymeric resins, Bond Elut PPL and another synthesized in our laboratory with an ocarboxybenzoyl moiety, were compared for solid-phase extraction (SPE) to detect lower concentrations of the eleven phenolics in natural waters. Higher recoveries were obtained using the functionalized polymeric adsorbents compared with Envi-Carb. When real samples were analysed, the synthetic adsorbent gave lower interference than Bond Elut PPL and phenol was determined at low levels with no humic and fulvic acid inter-ference when Na2SO3 was added. The linearity range for most compounds in tap water was 0.05–20 μg L−1 and the limits of detection were 〈35 ng L−1. Repeatability and reproducibility between days for real samples spiked at 0.1 μg L−1, expressed as relative standard deviation, were 〈8% and 10%, respectively.
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    The use of mobile phase pH and column temperature to reverse the retention order of enantiomers on chiral-AGP® (1998)
    Springer
    Chromatographia 47 (1998), S. 189-196 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Experimental design ; Mosapride ; Reversal of retention order ; Effect of pH and column temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Enantiomeric separation of mosapride and a structurally related compound was performed using chiral chromatography and experimental design. Unique effects of mobile phase pH and column temperature made it possible to control the elution order of the enantiomers when using Chiral-AGP as the solid phase. At a low mobile phase pH (〈6) the (R)-enantiomer of mosapride elutes before the (S)-form whereas the (S)-enantiomer elutes first at a high mobile phase pH (〉6). By using a mobile phase pH around 6, the column temperature could also be used to control the elution order of the enantiomers of mosapride. Similar effects of mobile phase pH and column temperature were obtained for the enantiomers of a structurally related compound, a metabolite (M1). Isocratic chromatographic systems made it possible to determine enantiomeric impurities less than 0.1% in the respective enantiomer of mosapride. The enantiomers of mosapride as well as the enantiomers of M1 could easily be separated simultaneously using Chiral-AGP and a simple gradient elution.
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    HPLC determination of colistin and aminoglycoside antibiotics in feeds by post-column derivatization and fluorescence detection (1998)
    Springer
    Chromatographia 48 (1998), S. 32-36 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Post-column derivatization ; Feeds ; Aminoglycoside antibiotics ; Colistin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Reversed-phase, HPLC methods employing post-column derivatization and fluorescence detection were developed for the determination of the peptide colistin and four aminoglycoside antibiotics in feeds. Extraction of the analytes was by sonication and shaking with dilute hydrochloric acid. Post-column derivatization was performed using orthophtaldialdehyde-2-mercaptoethanol chemistry. Assay of colistin was by using an acetonitrile-aqueous sodium sulphate-triethylammonium phosphate (pH 2.8) eluent. Aminoglycoside antibiotics:amikacin, kanamycin, gentamycin and neomycin were analyzed using a tetrahydrofuran-aqueous sodium sulphate-sodium pentanesulphonate-acetic acid mobile phase. The method was also applied to some pharmaceutical preparations. Preliminary results showed that the method can be adapted for the assay of the above antibiotics in meat and animal serum for residue and pharmacokinetic studies.
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    High-Performance liquid chromatographic separation of enantiomers of unusual amino acids possessing cycloalkane or cycloalkene skeletons on a chiral crown ether containing stationary phase (1998)
    Springer
    Chromatographia 48 (1998), S. 20-26 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Crownpak CR(+) Column ; Cyclic β-Amino Acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Direct reversed-phase high-performance liquid chromatographic methods were developed for the separation and identification of the enantiomers of mono- and bicyclic racemic β-amino acids:cis- andtrans-2-aminocyclopentane-1-carboxylic acids,cis- andtrans-2-aminocyclohexane-1-carboxylic acids,cis- andtrans-2-amino-4-cyclohexene-1-carboxylic acids,diendo- anddiexo-3-aminobicyclo[2.2.1]heptane-2-carboxylic acids anddiendo- anddiexo-3-amino-5-bicyclo[2.2.1]heptene-2-carboxylic acids. Enantioseparation was carried out by the application of a chiral stationary phase, Crownpak CR(+). The conditions of separation were optimized by changing the temperature, the flow rate and the pH of the mobile phase.
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    Enantiomeric separation of unusual secondary aromatic amino acids (1998)
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    Chromatographia 48 (1998), S. 53-58 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Gas chromatography ; Enantiomeric separation ; Chiral derivatization ; Unusual secondary aromatic amino acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary High-performance liquid chromatographic and gas chromatographic methods were developed for the separation of unusual secondary aromatic amino acids. Amino acids containing 1,2,3,4-tetrahydroisoquinoline, 1,2,3,4-tetrahydronorharmane-1-carboxylic acid and 1,2,3,4-tetrahydro-3-carboxy-2-carboline moieties were synthetized in racemic or chiral forms. The high-performance liquid chromatography was carried out either on a teicoplanin-containing chiral stationary phase or on an achiral C18 column. In the latter case the diastereomers of the amino acids formed by precolumn derivatization with the chiral reagents 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl isothiocyanate or 1-fluoro-2,4-dinitrophenyl-5-L-alanine amide were separated. The gas chromatographic analyses were based on separation on a Chirasil-L-Val column.
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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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    Determination of ketorolac enantiomers in plasma using enantioselective liquid chromatography. Application to pharmacokinetic studies (1998)
    Springer
    Chromatographia 48 (1998), S. 203-208 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ketorolac in plasma ; Enantiomer separation ; Pharmacokinetic studies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A direct HPLC method for quantification of the (R) and (S) enantiomers of ketorolac in human plasma for pharmacokinetics studies has been developed. Naproxen sodium [S(+) enantiomer] was used as an internal standard. Plasma samples (1 mL) were vortexed for 30 sec with methyltert-butyl ether, followed by centrifugation at 2000 g for 8 min. The aqueous phase was acidified (pH 1) by adding 1 mL of 2N HCl and back-extracted with 5 mL methyltert-butyl ether. The organic phase was evaporated, and the residue was dissolved in 200 μL of mobile phase. 25 μL were chromatographed on a α1-acid glycoprotein column (Chiral-AGP, 100×4 mm I.D.), using a mobile phase with 8.5% propan-2-ol in phosphate buffer (0.09M NaH2PO4.H2O, 0.01M Na2HPO4, 0.002M Dimethyloctylamine; pH 5.5). Calibration range was 20–20000 ng mL−1 for (R)- and (S)-ketorolac. The LOQ was 5 ng mL−1 for both enantiomers. The sensitivity could be extended to 1 ng mL−1 with the same precison by increasing the injection volume to 100 μL. The method is reproducible, accurate, and stereospecific. The inter-assay and intra-assay CVs were 〈11.40% and 〈9.30% for (R)- and (S)-ketorolac respectively. Under the conditions employed, no racemization was observed.
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    Optimisation of mobile phase pH in liquid chromatography. Application to fluorimetric detection of series of quinolones (1998)
    Springer
    Chromatographia 48 (1998), S. 251-257 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Mobile phase optimisation ; Fluorimetric detection ; Quinolones ; Dissociation constants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The dissociation constants of several quinolones in a 7% acetonitrile-water mixture are determined. A model describing the effect of pH on the retention of quinolones by an octadecylsilica stationary phase with a 7% acetonitrile-water mobile phase is proposed. The model uses pH values in the mobile phase instead of pH values in water and takes into account the effect of activity coefficients. Fluorescence of quinolones in the mobile phase is studied, and a chromatographic separation with fluorimetric detection is established. Detection limits for the proposed method range from 3 to 12 μg·L−1.
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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 
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    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 
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    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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    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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    Chiral recognition by molecularly imprinted polymers in aqueous media (1998)
    Springer
    Chromatographia 48 (1998), S. 197-202 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Molecular imprinting ; Molecular recognition ; Chiral recognition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Molecularly imprinted polymers were prepared using 2-vinylpyridine and/or methacrylic acid as functional monomers in a self-assembly imprinting protocol. The resulting polymers were analyzed in aqueous media, and the effects from the pH of the mobile phase and the degree of added organic solvent were investigated. The results are indicative of the importance of ionic bonds in conjunction with hydrophobic interactions in the formation of the complexes between the analyte and the polymers.
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    Dye-coated stationary-phases: A retention model for anions in ion-interaction chromatography (1998)
    Springer
    Chromatographia 48 (1998), S. 190-196 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-interaction chromatography ; Dye-coated reversed phase ; Retention model ; Experimental design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of inorganic anions (NO3 −, NO2 −, Cl−, Br−, I−, SO4 2−, S2O3 2−) by ion-interaction chromatography mediated with a specific dye has been investigated. Chromatography was performed on a LiChrospher RP-18 colum dynamically coated with crystal violet, using acetonitrile-water buffered with phthalate as the mobile phase. The presence of the dye in the eluent enabled indirect spectrophotometric detection of the analytes, which have no significant UV absorption. Retention data were collected for the different anions by varying the composition of the mobile phase according to a full factorial experimental design. A theoretical model for the retention of singly- and doubly-charged analytes, on the basis of the two main processes of ion-exchange and ion-pair formation, has been proposed and validated with the experimental data.
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    Wheat β-amylase behaviour regarding salt promoted adsorption processes (1998)
    Springer
    Chromatographia 48 (1998), S. 209-214 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Covalent chromatography ; Thiophilic and hydrophobic ligands ; Wheat β-amylase ; Salt promoted adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The behaviour of wheat β-amylase from crude extracts in chromatography on agarose gels substituted with different ligand types was investigated. The enzyme displayed high salt promoted adsorption onto thiophilic gels provided with sulfone-thioether and 2-thiopyridine ligands. Quantitative recovery of the enzyme was easily accomplished by elution with buffer in the absence of Na2SO4. The 3-(2-pyridylthio)-2-hydroxypropylagarose (PyS-gel) also allowed elimination of pigments present in the wheat extract. These pigments showed no adsorption onto the gel, thus regeneration is easily achieved, allowing its re-use. The enzyme also displayed strong salt-dependent adsorption onto adsorbents provided with pyridyldisulfide moieties, but in this case enzyme binding was due to its thiol content since elution was achieved mainly through reduction with DTT. When the enzyme was chromatographed on a series of hydrophobic alkyl ligands in the presence of 0.5 M sodium sulphate, it was partially adsorbed on pentylagarose and quantitatively adsorbed on hexyl-agarose, elution being easily performed by sodium sulphate-free buffer. This behaviour was markedly different from that towards phenyl-Sepharose, to which the enzyme was strongly adsorbed and which required much more drastic elution conditions.
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    Characterization of peak purity by fast multiscan circular dichroism detection (1998)
    Springer
    Chromatographia 48 (1998), S. 584-588 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Circular dichroism detection ; Multiscan detection ; Peak purity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method has been developed to detect inhomogeneity of apparently homogeneous peaks of very similar analytes. The method utilizes the rapid scan feature of state-of-the-art spectrometers/detectors that allow the recording of up to 30 spectra in a single chromatographic peak. Sensitivity and selectivity are enhanced by chiroptical/optical detection. Thus, identification of “front” and “rear” components of the peak can be carried out. The method is exemplified by mixtures of codeine, hydrocodone and oxycodone as analytes.
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    Determination of myristicin in rat serum samples using microbore high performance liquid chromatography with column-switching (1998)
    Springer
    Chromatographia 48 (1998), S. 365-368 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Microbore columns ; Column-switching ; Myristicin ; Serum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A microbore high-performance liquid chromatographic method with column-switching was developed for the analysis of myristicin from rat serum without prepurification. Deproteinization, fractionation, concentration and separation of analyte were carried out by appropriate switching of columns and using solvent mixtures. The method showed excellent precision, accuracy and speed with a detection limit of 10 ng mL−1 from 25 μL of serum. The total analysis time per sample was 25 min and the coefficients of variation for intra- and inter-assay were less than 1.8%.
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    Growth effects of a revenue-neutral environmental tax reform (1998)
    Springer
    Journal of economics 67 (1998), S. 287-316 
    Details
    ISSN: 1617-7134
    Keywords: endogenous growth ; environmental externalities ; environmental tax reform ; elastic labor supply ; optimal taxation ; E62 ; Q28 ; O41 ; D62
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract This paper analyzes tax-policy measures within a two-sector endogenously-growing economy with elastic labor supply. Pollution is either modeled as a side product of physical capital used as a production factor in the final-good sector or as a side product of production. The framework allows us to analyze the consequences of isolated tax changes or of a revenue-neutral environmental tax reform for economic growth. Although pollution does not directly affect production processes, it can be shown that a higher pollution tax as well as a revenue-neutral environmental tax reform boost economic growth, whereas a tax on capital, consumption, or labor reduces the long-term growth rate of the economy.
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    The government's time discount rate: Choices and consequences in a dynamic framework (1998)
    Springer
    Journal of economics 67 (1998), S. 265-285 
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    ISSN: 1617-7134
    Keywords: fiscal policy ; monetary policy ; time discount rate ; inflation target ; E52 ; E62
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract This paper considers a closed macroeconomy where the monetary authority pursues an inflation target and policy outcomes are the consequence of a Nash game between fiscal and monetary authorities. The specification of the macroeconomic framework is characterized by nonlinearities which lead to multiple equilibria with differing stability properties. Employing a calibrated model and simulations derived using the Mathematica package, the stability properties of the economy and the likely choice of equilibrium are examined. Within this framework, the dynamic consequences of different time discount rates for the fiscal authority are investigated, both in a world of certainty and also in a world of uncertainty. It is shown that, in a world of certainty, it will be optimal to choose the fiscal authority's time discount rate equal to the market rate of interest. However, depending on the degree of uncertainty in evaluating the time discount rates of consumers and of the fiscal authority, it may be appropriate to bias the fiscal authority's discount rate above or below the expected interest rate.
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    The accomplishment of the Maastricht criteria with respect to initial debt (1998)
    Springer
    Journal of economics 68 (1998), S. 93-110 
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    ISSN: 1617-7134
    Keywords: optimal control ; Maastricht criteria ; C61 ; E62
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract The reduction of government debt to 60% of the GDP in order to satisfy the requirements of the Maastricht Treaty for participation in the European Monetary Union is one of the primary economic-policy goals for most of the European Union countries. The first aim of the present paper is to characterize the optimal path of the primary surplus that leads to the achievement of this Maastricht target. Using optimal-control theory we are able to determine an upper bound of the public-debt-to-GDP ratio above which no retrenchment policy becomes effective. The second issue taken up is that of the sensitivity analysis with respect to the initial level of the debt-to-GDP ratio, the growth rate of the economy, the interest rate, the inflation rate, and the inverse of the velocity of the monetary base circulation.
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    Fiscal policy in an endogenous-growth model with public investment: A note (1998)
    Springer
    Journal of economics 68 (1998), S. 193-198 
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    ISSN: 1617-7134
    Keywords: endogenous growth ; welfare ; public investment ; fiscal policy ; O41 ; H20 ; E62
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract This note extends the basic endogenous-growth model by Barro [Journal of Political Economy (1990) 98: S103–S125]. It is supposed that the government pays lump-sum transfers to the representative household or levies a lump-sum tax, besides financing public investment. Growth and welfare effects of fiscal policy are studied for the competitive economy and the growth rate of the social optimum is compared with the one of the competitive economy.
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    Application of SPE for the HPLC analysis of taxanes fromTaxus cell cultures (1998)
    Springer
    Chromatographia 47 (1998), S. 25-34 
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    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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    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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    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 
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    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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    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 
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    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 
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    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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    The chromatographic behavior of arsenic compounds on anion exchange columns with binary organic acids as mobile phases (1998)
    Springer
    Chromatographia 47 (1998), S. 257-263 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion exchange chromatography ; Anion-exchange chromatography ; Arsenic compounds ; Flame atomic absorption detector
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Identification and quantification of arsenic compunds was performed with high- performance liquid chromatography (HPLC) and flame atomic absorption spectrometry (FAAS) as element-specific detector. Arsenous acid, methylarsonic acid, dimethylarsinic acid, arsenic acid, arsenobetaine, and arsenocholine were separated on two anion-exchange columns (Synchropak Q 300 and PRP-X 100) with different binary organic acids as mobile phases. The infleunce of chromatographic parameters, such as pH and the concentration of the mobile phase were investigated. An unusual chromatographic behavior of arsenous acid was observed when tartaric acid was used as mobile phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02466529
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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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    URL: http://dx.doi.org/10.1007/BF02466535
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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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    URL: http://dx.doi.org/10.1007/BF02466467
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  • 88
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    Highly selective antibody-mediated extraction of isoproturon from complex matrices (1998)
    Springer
    Chromatographia 47 (1998), S. 453-456 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Affinity chromatography ; Selectivity and capacity ; Isoproturon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary For the analysis of pesticides such as isoproturon in complex matrices the rate determining step is sample preparation. A novel solid-phase extraction system for isoproturon based on antibody mediated extraction has been developed. The isoproturon can be retained while the immuno-extraction column is washed with phosphate buffered saline and eluted using phosphate buffered saline/ethanol at low pH. The column can preconcentrate isoproturon from up to at least 1000 mL water and elute in 1 mL. Quantitative recovery of isoproturon from water, plasma and urine can be obtained and the proposed water assay can detect as low as 50 ng L−1 with a 50 mL sample, or 5 ng L−1 with a 1 L sample.
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    URL: http://dx.doi.org/10.1007/BF02466480
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    Experimental and statistical approach for validating and HPLC assay for the determination of vitamin a in flour and milk powder for children (1998)
    Springer
    Chromatographia 47 (1998), S. 716-720 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Vitamin A in flour and milk powder ; Method validation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An experimental and statistical approach is presented which enables, with a minimum of determinations, the validation of a high-performance liquid chromatographic (HPLC) method for the determination of vitamin A in milk powder and flour for children. The principal aspects of method validation are examined and discussed.
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    URL: http://dx.doi.org/10.1007/BF02467459
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  • 90
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    Group separation of organic nitrates on a new nitric acid ester NP-LC stationary phase (1998)
    Springer
    Chromatographia 47 (1998), S. 157-163 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Nitric acid ester phase ; Alkyl nitrates ; Group separation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The synthesis of a nitric acid ester NP-LC stationary phase (organonitrate phase), by nitrating a commercial polyol phase (Serva, Polyol Si 100, 5 μm) with mixed sulfuric-and nitric acid, is reported. The nitric acid ester bond is quite stable towards hydrolysis. To examine its possible use as a stationary phase for the group separation of alkyl nitrates, several bifunctional polar alkyl nitrates (di-nitrates, hydroxy-nitrates, keto-nitrates) have been synthesized. In order to simplify their names a new abbreviating nomenclature for multifunctional organic nitrates is presented. With our new stationary phase it is possible to separate mono-, di-, and hydroxy-nitrates as groups completely, a major advantage in sample preparation in the chemistry of smog formation. However a co-elution of di- and keto-nitrates is observed. A distinction of the latter two organonitrate groups is possible by gas chromatography-mass spectrometric detection (MSD). Apart from the fragment ion NO2 + (m/z=46 amu), which is nearly specific for alkyl nitrates, aliphatic di- and keto-nitrates show different characteristic fragment ions.
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    URL: http://dx.doi.org/10.1007/BF02466575
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    The use of an optimized RP-HPLC system as a molecular probe in QSPR studies of selected lipid classes (1998)
    Springer
    Chromatographia 47 (1998), S. 643-648 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Quantitative structure retention relationships ; Quantitative structure properties relationships ; Phospholipids ; Molecular probe
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The results of this study show that an optimized RP-HPLC system, in conjunction with molecular mechanics, can be used as a molecular probe to study both configuration and conformation of molecular species of selected phospholipid classes. Specifically, for phosphatidylcholine 18∶0/16∶0, stearic acid is attached to thesn-1 position and palmitic acid is attached to thesn-2 position of the glycerol backbone, for phosphatidylcholine with two monounsaturated fatty acids, the monounsaturated fatty acid attached to thesn-1 position can fold itself backwards on itself, thus allowing van der Waals interaction. Furthermore, it was found in the retention modelling that configurational descriptors alone did not suffice but had to be augmented with conformational descriptors. Nonlinearities were also detected, which could be handled by using a hybrid neural network-PLS regression strategy.
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    URL: http://dx.doi.org/10.1007/BF02467447
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  • 92
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    HPLC separation of hydrogenated derivatives of buckminsterfullerene (1998)
    Springer
    Chromatographia 48 (1998), S. 59-64 
    Details
    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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    URL: http://dx.doi.org/10.1007/BF02467517
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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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  • 94
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    A new validated high-performance liquid chromatographic method for the determination of EGIS-9933 in rat plasma (1998)
    Springer
    Chromatographia 48 (1998), S. 158-162 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; EGIS-9933 ; Solid phase extraction ; Rat plasma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new highly sensitive high-performance liquid chromatographic (HPLC) procedure for determination of EGIS-9933 (a newly developed anxiolytic compound) in rat plasma is described. A gradient, elution method with UV detection at 270 nm has been developed using a mobile phase of a mixture of A: methanol:acetonitrile 1:9 and B:0.5% triethilamine in water, the pH of B was adjusted to 3 with phosphoric acid. Solid phase extraction (SPE) was used for the sample preparation. The calibration was linear in the 10–10000 ng mL−1 concentration range. The limit of quantification was 10 ng mL−1. The bioanalytical method was validated according to internationally accepted criteria for biological samples.
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    URL: http://dx.doi.org/10.1007/BF02467535
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    Ion-pair HPLC determination of biogenic amines and precursor aminoacids. Application of a method based on simultaneous use of heptanesulphonate and octylamine to some foods (1998)
    Springer
    Chromatographia 48 (1998), S. 763-769 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-pair chromatography ; Food related-biogenic amines ; Heptanesulphonate ; Octylamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An ion-pair HPLC method based on the simultaneous use of heptanesulphonate and octylamine has been considered with the aim of optimizing the separation of four food-related biogenic amines (histamine, tyramine, 2-phenylethylamine and tryptamine) and related precursor aminoacids. On changing the eluant pH from 2.70 to 3.20 the capacity factor of precursor aminoacids decreased and those of the biogenic amines increased; pH 3 allowed an optimal separation. An increase of phosphate content, from 6.0 mM to 12.0 mM, shortened the capacity factors. The addition of octylamine to the eluant reduced the peak asymmetry (especially for histamine from 3.20 to 1.69). Some samples of cheese showed a concentration of total amines up to 1284.8 mg L−1; wines and beers showed a very similar total content, ranging from 0.5 mg L−1 to 27.2 mg L−1.
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    URL: http://dx.doi.org/10.1007/BF02467645
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    Supercritical fluid extraction of bile acids from bovine bile raw materials (1998)
    Springer
    Chromatographia 48 (1998), S. 785-789 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography-mass spectrometry ; Column liquid chromatography ; Supercritical fluid extraction ; Bile acids ; Bovine bile hydrolysates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The use of supercritical fluid extraction (SFE) as an alternative to conventional liquid extraction has been investigated to conventional liquid extraction has been investigated for the isolation of bile acids (cholic acid, deoxycholic acid and chenodeoxycholic acid) from the solid material obtained by bovine bile hydrolysis. Initial studies indicated that bile acids are not soluble in supercritical CO2, consequently the addition of the polar modifier methanol to the CO2 extracting fluid was evaluated. Quantitative recoveries (〉88.5%) were obtained for the bile acids in 20 min with 15% (v/v) methanol in CO2 at 220 atm and 70°C. A comparison of SFE with pyridine extraction was performed on samples of hydrolyzed crude bovine bile. The SFE method yielded recoveries higher than 82.7% compared with conventional liquid extraction. Moreover, SFE minimized sample handling, reduced the consumption of harmful solvents and provided conditions suitable for selective extractions of bile acids from bovine bile raw materials.
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    URL: http://dx.doi.org/10.1007/BF02467648
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    Enantiomeric resolution of melatonin ligands receptors by liquid chromatography on amylose chiral stationary phases (1998)
    Springer
    Chromatographia 48 (1998), S. 790-796 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chiral-enantiomeric separation ; Amylose-based chiral phases ; Melatonin analogues ; Tetrahydronaphthalenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Analytical HPLC methods using derivatized amylose chiral stationary phases were developed for the resolution of enantiomers of methoxy an ethyl tetrahydronaphthalenic derivatives, new agonist and antagonist ligands for melatonin receptors. Separation was by normal phase methodology with a mobile phase ofn-hexane-alcohol (methanol, ethanol, 1-propanol or 2-propanol) in various proportions, and a silica-based, amylose tris-(S)-1-phenylethylcarbamate (Chiralpak AS), or tris-3,5-dimethylphenylcarbamate (Chiralpak AD). The mobile phase and the chiral stationary phase were optimized for best resolution. The effects of concentration of alcohol, various aliphatic alcohols in the mobile phase were studied. The effects of substitution were analysed. Baseline separation (Rs〉1.5) was easily obtained in man cases.
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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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  • 100
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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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