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  • Column liquid chromatography  (117)
  • Springer  (117)
  • American Meteorological Society
  • 2010-2014
  • 1995-1999  (117)
  • 1990-1994
  • 1935-1939
  • 1997  (37)
  • 1996  (80)
Collection
Keywords
Publisher
  • Springer  (117)
  • American Meteorological Society
Years
  • 2010-2014
  • 1995-1999  (117)
  • 1990-1994
  • 1935-1939
Year
  • 1
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Heterocyclic aromatic amines (HAA) ; Electrospray MS-MS detection ; Selected reaction monitoring (SRM)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Sensitive and selective detection of the sixteen most abundant heterocyclic aromatic amines (HAA) has been achieved by application of high performance liquid chromatography-electrospray tandem mass spectrometry (HPLC-ESI-MS-MS) in combination with selected reaction monitoring (SRM). Detection limits between 0.1 and 50 ng mL−1 were established by use of HAA model solutions.
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  • 2
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Column switching ; Step-gradient elution ; Optimization ; Trace analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A computer spreadsheet application has been developed for the optimization of step-gradient elution conditions as applied in coupled-column RPLC for online clean-up and separation in the analysis of pesticide residues. The procedure is based on the experimentally determined retention behaviour of the analytes as a function of mobile phase composition. Retention and peak volumes of the analytes eluting under isocratic and one- and/or two-step gradient conditions can be calculated. For a given set of analytes, the spreadsheet systematically calculates the resolution of the least efficiently separated pair of peaks in the space defined by the eluotropic strengths of the mobile phases and the time at which the step-gradient takes place. The performance of the proposed procedure was tested and evaluated for the analysis of nine polar pesticides for which in a previous study adequate conditions had been found by computer-aided chromatogram simulation. the optimum conditions predicted by the procedure were in good agreement with those established experimentally and by simulation. The simultaneous production of data on retention, peak volume and resolution for a group of analytes under selected one- and/or two step-gradient elution conditions makes the calculation procedure highly productive and flexible in searching for and/or adjusting appropriate separation conditions.
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  • 3
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Hydrous zirconium oxide ; Porous polymer resin ; Disubstituted phenols ; ortho-Benzoic acid derivatives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A porous polymer resin loaded with hydrous zirconium oxide (Zr-gel) was evaluated as a stationary phase for the liquid chromatographic separation of disubstituted aromatic compounds. The prepared Zr-gel was used to separate disubstituted phenols andortho-substituted benzoic acid derivatives in reversed-phase mode. The retention time of catechol was greater than those of other disubstituted phenols; this implies that the Zr-gel has specificity for the phenolic hydroxyl group. The retention behavior ofortho-substituted benzoic acid derivatives on the Zr-gel was also evaluated in reversedphase mode using buffer. Phthalic acid was specifically retained in the vicinity of pH 6.0, which has been regarded as the equal adsorbic point. Similar behavior was also observed for salicylic acid, although the retention time of salicylic acid was less than that of phthalic acid. It seems that the specific retention behavior of hydrous zirconium oxide is a result of complexation with ligands such as hydroxyl and carboxyl groups. The results of this study have revealed that the retention mechanism of hydrous zirconium oxide is a combination of ion exchange and interaction based on complexation with ligands.
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  • 4
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Tryptophan ; Chiral separations ; Diode-laser polarimetric detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The combined utilization of photometric, fluorimetric and polarimetric detection liquid chromatography detectors in series for the identification and quantification of D-tryptophan and L-tryptophan was evaluated. Detection limits of about 1 μg were established with the range of linearity extending to about 100 μg. The relative standard deviation of the D-form and L-form tryptophan were 7.32 and 4.22%, respectively. The amount unknown of tryptophan enantiomers in the different mixtures was determined with an accuracy of 1.58% at the 40 μg injection level.
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  • 5
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Un-sulphated and sulphated surfactants ; Oligoethyleneglycol nonylphenyl ethers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Retention behaviour of un-sulphated and sulphated, oligoethyleneglycol nonylphenyl ether, anionic surfactants was investigated in normal-phase LC systems with chemically bonded amino stationary phase in organic mobile phases containing water and cetyl trimethylammonium bromide (CTAB). Addition of water to the mobile phase improves efficiency of separation and linearity of the dependences of logk′ versus number of oxyethylene units in the sulphated oligomers, so that it is possible to describe simultaneous effects of this number and of the concentration of CTAB on retention by a simple equation. In this system, it is possible to separate lower sulphated and un-sulphated oligomers in a single run in 10–15 min under isocratic conditions.
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  • 6
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Electrothermal atomic absorption spectrometry ; Vitamin B12 analogues ; Cobalamins and cobalt ; Meat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The coupling of liquid chromatography and electrothermal atomic absorption spectrometry (LC-ETAAS) lowers the detection limit for identification of vitamin B12 analogues. Cobalamins and aqueous cobalt (II) were separated by reversed-phase liquid chromatography using a linear gradient: 26∶74 (v/v) methanol:0.05 M phosphate buffer (pH 4.2) to 50∶50 mixture over 8 min. The vitamins were quantitatively determined in the column effluent by measuring total cobalt by ETAAS. The analysis of meat and liver extracts by LC-ETAAS showed that the matrix did not interfere with the determination of cobalt. Hence, recoveries of cobalt in spiked meat and liver samples were satisfactory.
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  • 7
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    Chromatographia 42 (1996), S. 405-408 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Meropenem in rat plasma ; Column-switching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The purpose of this study was to develop a columnswitching HPLC method for the determination of meropenem in plasma. This method showed excellent precision and accuracy with good sensitivity and speed. The total analysis time per sample was less than 20 min and the mean coefficients of variation for intra- and inter-assay were less than 4.0%. The method has been successfully applied to plasma samples from rats receiving an intraperitoneal injection of meropenem.
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  • 8
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Thiol drugs ; Pre-chromatographic derivatization ; 1,1′-[ethenylidenebis(sulfonyl)]bis-benzene reagent
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The use of 1,1′-[ethenylidenebis(sulfonyl)]bis-benzene as a pre-chromatographic reagent for LC analysis of thiol drugs is proposed. The reagent reacts rapidly (2 min) under mild conditions (pH 7.5, ambient) with thiol drugs and the resulting adducts can be chromatographed under reversed-phase conditions (C-18 column). Excess reagent can be removed from the reaction mixture by simple liquid-liquid extraction with chloroform. The HPLC method using UV detection was successfully applied to the analysis of reduced glutathione (GSH), N-acetylcysteine, N-2-mercaptopropionylglycine and captopril in their commercial formulations.
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  • 9
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; 2-Arylpropionic acids ; Barbituric acids ; Benzodiazepines ; Cellulose tris(4-methylbenzoate) chiral stationary phase ; Reversed-phase mode ; Chiral recognition mechanisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A newly developed reversed-phase chiral stationary phase, cellulose tris(4-methylbenzoate), known as Chiralcel OJ-R, has been successfully applied to the direct resolution of the enantiomers of several nonsteroidal anti-inflammatory drugs belonging to the profen group. Among the five barbituric acids tested, the chiral resolution of mephobarbital is especially high. The Chiralcel OJ-R column also proved quite efficient for the enantiomeric resolution of a few representatives of the benzodiazepine group. Variations of mobile phase conditions based on acetonitrile and/or methanol were tested. The results obtained are briefly compared with separations performed using a Chiralcel OJ column under normalphase conditions.
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  • 10
    ISSN: 1612-1112
    Keywords: Liquid-liquid and liquid-solid extractions ; Column liquid chromatography ; Mass spectrometry detection ; Flavonoids inPhillyrea angustifolia leaves
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Liquid-liquid (LLE) and liquid-solid extraction (LSE) procedures were developed to identify polyphenols in phillyrea (Phillyrea angustifolia L.) leaves. The liquidsolid extraction, carried out by using two serial Bond-Elut® CH and Bond-Elut® SAX cartridges allowed the collection of both polyphenols and soluble carbohydrates during a single extraction of leaf. This method seems to be suitable for both phytochemical and physiological study of the species, allowing the identification of two classes of organic compounds which have a central role in the metabolism of phillyrea plants. A method of isolation and concentration of polyphenols for further molecular characterization, using centrifuge chromatography, was also developed. Molecular characterization, carried out by UV-Vis spectrophotometry and mass spectrometry, demonstrated the presence of compounds with interesting biological activity, i.e. flavonoids and oleuropein derivatives. The soluble carbohydrate composition of phillyrea leaves did not substantially differ from that ofOlea europaea L. leaves, except for a higher mannitol/glucose ratio. This carbohydrate distribution may be linked to the evolution pattern of this species which usually grows in severely stressed environments.
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  • 11
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; On-line liquid chromatography-mass spectrometry ; Neutral and acidic cannabinoids ; Hashish samples
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This paper reports the use of liquid chromatography for the separation and determination of the major cannabinoids extracted from hashish samples. The direct coupling to the mass spectrometer enables the selective identification both of neutral and acidic cannabinoids. The developed method does not require any preliminary derivatization and should, therefore, be of interest in forensic analysis for simple and unequivocal determination of hashish constituents.
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  • 12
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Non-linear adsorption isotherm ; Simulation of chromatographic peak profiles ; Separation of optical isomers ; Non-racemic mixtures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This article discusses the effect of solute association on the apparent adsorption isotherm and on the chromatographic peak profile. The modelling performed has shown that dimerization of a solute in a chromatographic system gives rise to an apparent adsorption isotherm of the non-linear type. This results first of all in peak broadening. Tailing or a fronting can be observed depending on the relative retention of the monomer and the dimer. Secondly, the retention of the solute depends on the amount of sample because of the non-linear character of the adsorption isotherm. As a result, an excess of one of two analytes with absolutely identical adsorption properties i.e. optical isomers, can be separated in such chromatographic systems by considering that the sample contains non-equal amounts of two analytes. The phenomenon is illustrated by simulated chromatograms of the separation of non-racemic mixtures of enantiomers.
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  • 13
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Hydrous zirconium oxide ; Porous polymer resin ; Silica gel ; ortho-Benzoic acid derivatives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Silica gel loaded with hydrous zirconium oxide (Zr-gel-S) has been prepared and the influence of the base material on the retention behavior ofo-phthalic acid on the hydrous zirconium oxide was evaluated. The retention behavior of the acid on the Zr-gel-S was compared with that on Zr-gel-5, the polymer-based Zr-gel. Comparable retention behavior,i.e. maximum retention in the vicinity of pH 6, which has been regarded as the equal adsorbic point, was observed for both types of Zr-gel, although there was a large difference in the retention times. The difference in retention on the two types of Zr-gel could be ascribed to nature of the base material. The results in this experiments showed, however, that the specific behavior at pH 6 was an essential characteristic of hydrous zirconium oxide and was not related to the influence of the base materials.
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  • 14
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Sterols, tocopherols, retinols and carotenes ; Dairy products
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary We have previously described a normal-phase HPLC method for the simultaneous determination of α, β, γ and δ tocopherol, thecis andtrans isomers of retinol, and total carotenes in different Italian cheeses and milk. In this paper we describe a reversed-phase HPLC method using solely methanol as the mobile phase for the determination of α-tocopherol, β-+γ-tocopherols, total retinols, cholesterol, β-sitosterol, campesterol and stigmasterol, and α- and β-carotene. The method developed has been applied to some new dairy products such as natural Quark, with olive, basil or banana and to processed cheese with tomato and the results have been compared with the corresponding results obtained by the normal-phase method. The conclusion is that more complete evaluation of the tocopherol, retinol, carotene and sterol content of dairy products, especially when vegetables and fruits are present, is necessary and can be obtained using both the normal- and reversed-phase HPLC methodologies.
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  • 15
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Diode-array detection ; Particle beam mass spectrometric detection ; Pesticides in water ; On-line solid-phase extraction (SPE)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A group of pesticides has been determined by liquid chromatography with diode-array detection (DAD). The coupling of a particle-beam (PB) mass spectrometer to the outlet of the DAD enabled the identities of the pesticides to be confirmed from mass spectra obtained by electron impact ionization. On-line trace enrichment of 200 mL of sample with a PLRP-S precolumn enabled most pesticides to be determined in real samples at levels between 0.2 and 5 μg L−1 and with limits of detection (LOD) between 0.05 and 0.5 μg L−1. In the analysis of real samples, one of the pesticides studied was determined by DAD and its identity was confirmed by comparison of PB mass spectra. The use of PB-MS also enabled the detection of non-target compounds.
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  • 16
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Capillary electrophoresis ; Phenolic compounds ; Water samples
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A comparative study of high-performance liquid chromatography (HPLC) and capillary zone electrophoresis (CZE) for determination of eleven EPA priority phenols in water samples is discussed. The repeatability, linearity and detection limits of both methods are compared. A solid-phase extraction method using a highly cross-linked styrene-divinylbenzene copolymer sorbent is used for the off-line preconcentration process in order to determine these compounds in water at low levels. Both methods are used to determine phenolic compounds in Ebro river and industrial waste water. Identification was achieved by comparison of the UV spectra corresponding to the different peaks, acquired with a diode-array detector, with those in a spectral library.
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  • 17
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polycyclic aromatic hydrocarbons ; Waste waters ; Sewage sludge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A modified solid-phase extraction technique using sonication of the adsorbent material instead of the elution normally applied has been compared with two conventional liquid-liquid extraction procedures for the determination of the 16 EPA PAHs in municipal waste waters by means of HPLC coupled with fluorescence detection. Liquid-liquid extraction with cyclohexane proved to be the most efficient and simplest procedure. Clean-up of the waste-water extracts was not considered necessary, because of the high chromatographic resolution of the column and the selectivity of the fluorescence detector. Different organic solvents were also compared for ultrasonic extraction of PAHs from sewage sludge. The best results were obtained by use of acetonitrile. Clean-up of sewage-sludge extracts was not found necessary for accurate quantification of the major PAH components with fluorescence detection. The precision of the whole analytical procedure from extraction to the final determination of PAHs was satisfactory for both waste-water and sewage-sludge samples.
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  • 18
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    Chromatographia 43 (1996), S. 117-123 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-exchange chromatography ; Ion-exchange mechanism ; Optimization of alkali and alkaline earth separation ; Crown ether complexing reagents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The elution behavior of alkali and earth alkaline cations has been studied on a newly synthesized weak cationexchanger (WCX). Applying this stationary phase isocratic separation of these cations is possible. The dependence of retention on competing ion concentration is described via a simple model. The influence of crown ethers as well as organic eluent additives on selectivity and peak efficiency is demonstrated. With optimized separation such cations can be determined with detection limits of about 0.5 ppm using a conductivity detector without ion suppression.
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  • 19
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    Chromatographia 43 (1996), S. 143-148 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Micellar liquid chromatography ; Ion-exchange-induced stationary phase ; Dansyl amino acids (Dns-AAs) ; Fluorescence enhancement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The retention behavior of dansyl amino acids in micellar liquid chromatography has been examined by using ionexchange-induced stationary phases. Several parameters affected the retention of the analytes, including the type and concentration of micellar agent and modifier ion and the concentration of acetonitrile in the mobile phase. The order of elution of dansyl amino acids obtained with the micellar mobile phase was very different from that observed in conventional reversed-phase liquid chromatography. Fluorescence intensities of some dansyl amino acids were enhanced by the micellar mobile phase.
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  • 20
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Experimental design ; Direct chiral resolution ; Omeprazole ; Hydroxy-omeprazole
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A strategy for the optimisation of direct chiral separation of omeprazole and a metabolite, hydroxi-omeprazole, in reversed phase liquid chromatography is described. A factorial design was used, where mobile phase pH, concentration of a mobile phase modifier, ionic strength and column temperature were tested as the variables and enantioselective retention, column efficiency and asymmetry factor as the responses. The experimental results were evaluated with multivariate analyses, which demonstrated that the column temperature and content of mobile phase acetonitrile were by far the most important variables. The enantiomers of omeprazole and one of its metabolites were baseline resolved within 15 minutes. The optimised chromatographic system was used for a separation of the enantiomers of omeprazole and its main metabolite in a patient plasma sample.
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  • 21
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chemiluminescence detection ; Tiopronin ; Thiols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In previous pharmacokinetic studies tiopronin, a drug used for effective treatment of cystinuria and rheumatoid arthritis, and its metabolite 2-mercaptopropionic acid were analysed by conventional liquid chromatography with pre- and post-column derivatization and UV detection. Now a novel HPLC-coupled chemiluminescence-flow-injection analysis (CL-FIA) method has been developed for the determination of tiopronin and 2-mercaptopropionic acid in urine. The method is based on chemiluminescence from a Ce(IV) oxidation system sensitized by quinine, as proposed earlier by this group, and flow-injection analysis. The method, which has the advantages of high sensitivity and selectivity, simple sample treatment and prompt production of results, has also been preliminarily adapted for pharmacokinetic study of tiopronin in urine.
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  • 22
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; UV and electrochemical detection ; Particle beam-mass spectrometry ; Fat-souble vitamin ; Standard-bore and narrow-bore columns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The application of different detection techniques; UV, electrochemical (ED) and particle beam-mass spectrometry (PB-MS) for the high-performance liquid chromatography analysis of fat-soluble vitamins were studied. Separation of all compounds examined was performed using both C8 standard-bore and narrow-bore columns for UV and MS detection, whereas in the case of HPLC-ED, a C8 standard-bore column only was used. Detector responses were studied in terms of linear range, detection limit and precision. The HPLC methods with UV, PB-MS and electrochemical detection were applied to the assay of vitamins A and E in an infantformula, powdered-milk sample. Recovery studies showed good results both for vitamins A and E, within-run precision being 2–4% for LC-UV and LC-ED techniques. In addition, excellent aggrement between the results obtained with the detection systems explored was found.
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  • 23
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chemically bonded silica gel ; Mixed solvents ; Steroids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The chromatographic behaviour of 30 estradiol and estrone derivatives has been studied on diol, amino- and cyanopropyl silica gel stationary phases with non-aqueous mobile phases. The slopes of linear relationships between the logarithm of the retention factor and logarithm of the volume fractions of the polar components of the binary eluents have been calculated and are discussed in relation to the characteristics of the solute, eluent and stationary phase. An equation for testing the separation efficiency of stationary phases has been derived.
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  • 24
    ISSN: 1612-1112
    Keywords: Thin layer chromatography ; Column liquid chromatography ; Radioimmunoassay ; Cortisol ; Guinea pig ; Urine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In order to collect urinary samples from unrestrained guinea pigs, animals were kept in their familiar home cages with wood shavings for bedding. Cortisol was removed from shavings by a simple washing step, and an attempt was made to measure its concentrations by high performance thin-layer chromatography (HPTLC), high performance liquid chromatography (HPLC), or thin layer chromatography/radioimmunoassay (TLC-RIA). After intramuscular administration of 25 mg cortisol, cortisol excretion increased from about 20–30 μg/day to 400–500 μg/day (HPTLC: 531 μg/day, HPLC: 493 μg/day; TLC-RIA: 394 μg/day). Similarly, the treatment of the animals with 20 IU ACTH resulted in an augmented cortisol excretion, with mean values of 294 μg/day (HPTLC), 256 μg/day (HPLC) and 143 μg/day (TLC-RIA), respectively. The present study shows, for the first time, that cortisol excretion in unrestrained laboratory animals can be determined. Whilst the cortisol values measured by HPTLC and HPLC agree, the amounts measured by TLC-RIA were significantly lower. These differences are probably due to the presence of substances in urine or shavings which interfere with the radioimmunological determination. Hence, cortisol should be determined either by HPTLC or HPLC. Beside having a desirable specificity, these methods are more suited than TLC/RIA for steroid analysis since they confer the possibility of measuring additional steroids (e.g. precursors and/or metabolites of cortisol) in a single urine extract. This is especially the case for the HPTLC method since substances can be transformed into fluorescent derivatives.
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  • 25
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    Chromatographia 44 (1997), S. 257-262 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Microchromatography ; Raman spectroscopy ; Deuterated solvents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A detector for microchromatography in which Raman spectroscopy is used to identify the eluted species has been developed. The detector is designed to be applicable to a wide range of compounds without requiring the presence of a chromophore. Its use is illustrated in the analysis of nitro compounds on a 250 μm i.d. column. Raman spectra of each of the compounds could be identified as they passed the detector. The advatages of the use of fully deuterated solvents are demonstrated by the analysis of nitrobenzenes in methanol/water mobile phases. The detection limit for nitrobenzene using the Raman line at 1342 cm−1 was 75ng.
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  • 26
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Dipyridamole injection ; Stability studies ; Degradation products
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The development and subsequent validation of an isocratic high-performance liquid chromatographic (HPLC) procedure employing ultraviolet (UV) detection for the determination of degradation products in Dipyridamole Injection is reported. The development of this assay involved the evaluation of several factors including buffer type, ionic strength, pH, organic composition, and column type. The described method is simple, reproducible, accurate, and selective. The precision, relative standard deviation (RSD), amongst five sample preparations for total degradation products was not more than (NMT) 10.2 %, while the individual degradation products were NMT 12.1%. Intermediate precision, as determined from fifteen sample preparations, generated by two Analysts on different HPLC systems over three days, exhibited an RSD for total and individual degradation products of 8.2 % and NMT 27.5 %, respectively. The mean absolute recovery of dipyridamole using the described method is 102.1±1. 9%, (mean±SD, n=12) over the concentration range of 0.03 % to 5.0 % of its label claim of 5 mg mL−1. The limit of detection and limit of quantitation were 0.1 and 0.3 μg mL−1, respectively. The linearity of the peak response was verified with respect to dipyridamole concentration over a range of 0.3 and 50 μg mL−1 (0.03 % to 5.0 % label claim). The Standard and Assay Preparations are stable for up to 48 hours at room temperature. The selectivity was evaluated by subjecting the finished product (Dipyridamole Injection) to thermal, acidic, basic, oxidative and fluorescent radiation stress conditions. No interference in the analysis of degradation products was observed, showing the method is stability-indicating.
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  • 27
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    Chromatographia 44 (1997), S. 295-302 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Open tubular columns ; Weak cation-exchange stationary phase ; Biogenic amines ; LIF detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The preparation and performance of a weak cation-exchange stationary phase for Open Tubular Liquid Chromatography (OT-LC) was investigated. The stationary phase was prepared in 5.4 μm I.D. fused silica capillaries byin situ photopolymerization of a mixture of silicon acrylate and acrylic acid. The influence of pH, counter ion concentration and organic modifier concentration of the mobile phase on the retention was studied with catecholamines as test solutes using LIF detection. Other biological amines like amino acids, small peptides and nucleic acid derivatives could be separated on this stationary phase as well. The kinetic performance of the stationary phase was studied with several cations and neutral solutes.
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  • 28
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    Chromatographia 44 (1997), S. 427-430 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Mebeverine in dosage forms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple and rapid, high performance liquid chromatographic (HPLC) procedure for determination of mebeverine in dosage forms (tablet and liquid) is described. Reversed-Phase chromatography was carried out using a mobile phase containing 0.05 M ammonium acetate buffer and acetonitrile, [(45%, v/v) pH 5.2] with UV-detection (263 nm). Replicate regression analyses of three standard plots in the concentration range of 0.5–10 mcg mL−1 obtained on three different days gave a correlation coefficient 〉0.9995 and the coefficient of variation of the slopes 〈2.2%. The assay was precise within day and between days as indicated by ANOVA test. The recoveries from 10 replicate tablets of two commercial mebeverine brands and liquid were in order 99.3, 100.5 and 100.1% of the label amount and their coefficient of variations were 1.41, 0.89 and 0.69%, respectively. The limit of quantitation of mebeverine was 5 ng mL−1.
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  • 29
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Indirect separation ; Chiral derivatization ; Stable CDA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new chiral derivatizing agent (CDA) (1S, 2S) N-[(2-isothiocyanato)-cyclohexyl)-pivalinoyl amide ((S,S)-PDITC) is described. The CDA is available from 1,2-diamino cyclohexane (DACH) via a straightforward synthesis in both the (R,R) and (S,S)-configuration and can serve as a highly selective, stable reagent for the indirect resolution of chiral primary and secondary amines, amino acids and thiol compounds. The resulting diastereomeric thioureas and dithiocarbamates can be separated by simple RP-HPLC as demonstrated with a number of pharmaceutically important examples of amines and amino alcohol-type drugs. The latter diastereomers are compared with the well-established GITC derivatized compounds. The separation factors (α) of the diastereomeric thioureas range between 1.03 and 2.08 and were usually higher than those of the GITC derivatives. The chemical stability of the PDITC derivatives is excellent due to the absence of hydrolyzable ester groups— considered an advantage compared to GITC derivatives.
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  • 30
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Octadecyl titania ; Hydride surface ; Hydrosilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The silanization/hydrosilation bonding method is tested on both a laboratory synthesized and commercial titania. The laboratory titania made by the sol-gel process shows evidence of residual organic material that is removed by an initial acid hydolysis followed by bonding of the hydride (triethoxysilane) under acidic conditions. DRIFT and solid state CP-MAS NMR studies are used to confirm the formation of the hydride layer on the titania and the success of the hydrosilation process for attaching an organic moiety (1-octadecene) to the surface. Chromatographic testing, primarily on the commercial titania based C-18 phase, indicates good reverse phase properties and few residual OH groups, either Ti−OH or Si−OH, as determined by the symmetrical peak shapes obtained for anilines and alkylphenylamines using mobile phases with no buffers or masking agents in the aqueous component.
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  • 31
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Electrospray ionization mass spectrometry ; Micropellicular poly-styrene/divinylbenzene ; Peptides and proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Short columns packed with highly crosslinked 2.3 μm poly-styrene/divinylbenzene (PS/DVB) particles were used for rapid and efficient separation of proteins and peptides by reversed-phase high-performance liquid chromatography at elevated temperatures. Enhancement of the diffusivities of the sample components at elevated temperatures together with the short diffusion pathlength with the micropellicular polymeric stationary phases were responsible for high efficiency, high speed of analysis, and short column regeneration times. Underivatized PS/DVB beads as well as PS/DVB microspheres which have been modified with polyvinylalcohol or octadecyl chains on the surface were synthesized, employed, and compared to HY-TACH-C18, a commercially available micropellicular octadecyl-silica stationary phase, for the separation of proteins, octapeptides and tryptic protein digests. Highest performance was obtained with the silica- and PS/DVB-based octadecyl stationary phases, which exhibited similar column efficiencies but different selectivities for proteins and peptides. The minimum detectability at 214 nm and the maximum loading capacity for ribonuclease A using analytical 30×4.6 mm I.D. columns were 10 ng (0.6 pmol) and 1 μg, respectively. Finally, reversed-phase HPLC with a 60×2 mm I.D. narrow-bore column packed with micropellicular octadecyl PS/DVB was coupled successfully to electrospray mass spectrometry at a flow-rate of 0.15 mL min−1 and on-line full-scan mass spectra for molecular mass determination and identification of proteins in the lower picomol range were obtained.
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  • 32
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Column-switching ; Parathion, and metabolites in serum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new high-performance liquid chromatographic method with column-switching has been developed for the simultaneous determination of parathion and its metabolites such asp-nitrophenol and paraoxon in serum. Serum samples were injected onto a precolumn packed with LiChroprep RP-8 after simple dilution with 20% phosphoric acid. Polar plasma components were washed with 0.02 M phosphate buffer (pH 3.0). After valve switching, the concentrated compounds were eluted in back-flush mode and separated on a Ultracarb ODS 30 column with a gradient of acetonitrile −0.01 M phosphate buffer (pH 3.0) as mobile phase. The method showed excellent precision, accuracy and speed with detection limit of 0.1 μg mL−1. Total analysis time per sample was 〈40 min and coefficients of variation for intra-and inter-assay were 〈4.5%.
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  • 33
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    Chromatographia 44 (1997), S. 497-504 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Gas chromatography-mass spectrometry ; Column liquid chromatography ; Polycyclic aromatic hydrocarbons ; Food analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Several separation and detection methods for polycyclic aromatic hydrocarbons (PAHs) in smoked chicken by GC and HPLC were compared. With HPLC and a gradient solvent system, all 16 PAHs could be simultaneously separated and detected by fluorescence with seven settings of programmable wavelength (excitation/emission). The presence of impurities in smoked chicken could interfere with the subsequent identification and quantification of PAHs by HPLC. With GC and a temperature programming method, all 16 PAHs could be separated and the PAHs in the chicken sample could be detected with an ion-trap mass spectrometer even in the presence of fat-or PAH-like impurities. Nine PAHs were identified by the former method while fourteen PAHs were identified by the latter method. The retention times by HPLC were shorter than those by GC, also, the former had better separation for most PAHs than the latter.
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  • 34
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Computer optimization of separation ; Multisolvent mobile phases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary “Osiris” optimization software was usedfor optimizing separations with nonaqueous or partially aqueous mobile phases, consisting of 2, 3 or 4 solvents. For nonaqueous eluents used in Nonaqueous Reversed Phase Liquid Chromatography (NARP-LC), classical transfer rules cannot be used to determine isoeluent mobile phase compositions that are generally the starting point of most of the optimization procedures. The ability of this software to determine isoeluent compositions under NARP conditions is demonstrated. This determination is performed by modeling the solute retention from different sets of two gradient runs, each set being carried out for each binary mobile phase studied. The application of retention models to nonaqueous mobile phases is discussed in terms of the accuracy of the predicted retention times. In addition, it is shown that these sets of gradient runs allow selection of the best composition space for the optimum composition search without requiring additional runs. It is demonstrated that such a selection procedure greatly reduces the number of preliminary experiments.
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  • 35
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; RP chromatography ; Polystyrenes ; Mixed solvents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The reversed phase behaviour of high molecular mass polystyrenes was investigated on a C18 bonded phase column using acetonitrile as the polar mobile phase component and dichloromethane, chloroform and carbon tetrachloride, as separate nonpolar components. Solvent solubility compositions, elution compositions and resolutions of the various molar mass polystyrenes were measured and compared for each of the three mobile phases. Anomalous behaviour of the polystyrenes was not observed in any of the three mobile phases and only minor differences in resolution were observed. By comparing these results with previously published work, it is suggested that any mobile phase component that is both nonpolar and a good solvent for the polymer can be combined with acetonitrile for effective separations of polystyrenes by mass and that it is the poor solvent component of the mobile phase that is responsible for the anomalous behaviour that is sometimes observed in this type of chromatography.
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  • 36
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chiral separations ; Calcium channel antagonists ; On-line liquid chromatography-mass spectrometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An HPLC-CSP method has been developed for the separation of enantiomers of verapamil and gallopamil using the improved version of the α1-acid glycoprotein, chiral stationary phase as selector with a volatile mobile phase. The results of the investigation provide the conditions which allow direct coupling to a mass spectrometer. In addition, the simultaneous enantioseparation of both the enantiomeric pairs of verapamil and gallopamil was achieved.
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  • 37
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Substituted benzenes ; Solubility parameter ; Substituent constant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A quantitative structure-retention model derived from the concept of hydrophobic substituent constant (π) and the total solubility parameter (δT) has been established. It has been used to predict successfully the retention behavior of a number of solutes on various columns in several different eluents. The experimental results indicate that the model can be employed for the prediction of retention of substituted benzenes in a large volume fraction range of mobile phase. In addition, the physical meaning of the sign and the influence of the coefficients of the model on the retention process had been discussed together with the dependence of these coefficients on the composition of mobile phase.
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  • 38
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Fullerences ; Alkyl bonded silica phases ; Retention vs. column temperature ; CP-MAS NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The temperature-dependency of the separation of fullerenes in liquid chromatography (LC) has been examined using various alkyl bonded stationary phases. It has been found that a maximum retention temperature exists with long alkyl bonded stationary phases, whereas there is no similar effect with the newly synthesized alkyl bonded phases which have two phenyl groups at the base of the bonded phase. The interpretation of the retention behavior of fullerenes in the low temperature region on alkyl bonded stationary phases is discussed using information obtained by CP-MAS solid-state NMR spectroscopy and LC.
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  • 39
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    Chromatographia 42 (1996), S. 683-689 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chiral stationary phase ; Enantionary phase ; Enantiomer separation ; Amino acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Two chiral stationary phases (CSP-1 and CSP-2)) were synthesized by covalent bonding of aminopropylsilica (APS) to (a) 1-fluoro-2,4-dinitrophenyl-5-L-alanine amide (Marfey's reagent), followed by end-capping of underivatized amino groups of APS with trifluoroacetic anhydride (CSP-1), and (b) by reaction of APS with 1-fluoro-2,4-dinitrophenyl-5-L-phenylalaninetert. butyl ester, followed by cleavage of the tert. butyl ester by trifluoroacetic acid and end-capping of underivatized amino groups of APS withn-butyryl chloride (CSP-2). Both CSPs were found to be suitable for the chiral resolution of 2,4-dinitrophenyl and 3,5-dinitrobenzoyl-DL-amino acid esters by liquid chromatography using mixtures ofn-hexane andiso-propanol as eluents. Racemic 2,2,2-trifluoro-1-(9-anthryl)ethanol was also resolved on CSP-2.
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  • 40
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Calcium and lead phosphate hydroxyapatite ; Globular proteins ; Colecalciferol (Vitamin D3) and related compounds ; Organophosphorus insecticides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A qualitative study using two new stationary phases (spherical aggregates of calcium phosphate hydroxy-apatite and lead phosphate hydroxyapatite) as adsorbents in high performance liquid chromatography has achieved the separation of: a standard mixture of globular proteins; colecalciferol and related compounds (produced by irradiation and heating of provitamin D3); and a mixture of organophosphorus insecticides used in agriculture.
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  • 41
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    Chromatographia 42 (1996), S. 199-205 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Negative ion CI mass spectrometry ; Oxidizedd-limonene ; Contact allergenic compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A detailed chemical analysis and quantification of oxygen-containing monoterpenes in auto-oxidizedd-limonene was performed. Some of these, e.g. the cis- and trans-isomers of limonene-2-hydroperoxide, have previously been shown to exhibit strong contact allergenic properties. GC-MS with chemical ionization in negative ion mode was shown to be a successful method for the identification and determination of the molecular weight of chemically unstable limonene hydroperoxides. An HPLC method for isolation of individual compounds in auto-oxidizedd-limonene is presented. Two different stationary phases were used in normal phase mode, cyanopropyl- and diamino-modified silica. The method described can be used for the isolation of individual contact allergens in sensitization experiment vehicles, such as petrolatum and olive oil. This makes it possible to study whether test compounds, such as hydroperoxides, are chemically stable during a sensitization experiment.
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  • 42
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Stationary phases ; TiO2 ZrO2 AlO3 ; Separation of basic compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Chromatographic properties of silica, alumina, titania and zirconia have been investigated in normal phase mode in the separation of test mixtures of basic, neutral and acidic compounds. In contrast to silica the chromatographic behaviour revealed the basic properties of the alumina, titania and zirconia surfaces. Therefore, separation of basic compounds on these packings seems very promising. Lypophilic packings have been synthesized by modification of titania, zirconia and alumina with organosilanes and polymers and tested for the separation of basic compounds and proteins. High hydrolytic stability of the modified packings was observed during separations with strong alkali and acidic eluents.
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  • 43
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Column-switching technique ; Rabbit plasma ; Ampicillin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The purpose of this study was to develop a simple and fast analytical method for quantitation of ampicillin in rabbit plasma, suitable for analysis of large numbers of samples collected from experimental animals. The concentration of ampicillin in rabbit plasma was determined utilizing ion-pair reverse-phase high performance liquid chromatography (HPLC) with UV detection and a column switching technique. Plasma samples were treated with a perchloric acid solution to precipitate proteins and centrifuged to pellet the precipitated proteins. Cephalexin was used as an internal standard. The C18 precolumn was placed in the injector loop of the Rheodyne injector. Samples were injected with the injector in the load position and the precolumn was washed free from interfering compounds. When the injector was switched to the inject position, the mobile phase was passed through the precolumn taking relatively pure compounds onto the analytical column. The limit of quantitation was established to be 400 ng mL−1 of plasma. The standard curves were linear over the range of ampicillin concentrations assayed, 400 to 10,000 ng mL−1 of rabbit plasma, and had a mean regression coefficient of 0.9962 (±0.0043). Intra-day variability was determined using six replicates of controls (low and high) analyzed on a single assay. The percent of relative accuracy for low and high controls were 5.67 and 1.12, respectively. Inter-day variability was determined over a four day period analyzing replicates of each control. The percent of relative accuracy for low and high controls were 4.33 and 1.63, respectively.
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  • 44
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Size exclusion chromatography ; Pore structure ; Nitrogen sorptometry ; Zirconium oxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The pore structures of zirconium oxide particles prepared by two different methods (PICA and Oil Emulsion processes) are compared. Nitrogen sorptometry and size exclusion chromatography are used to characterize the two different types of particles. Significant and unexpected differences were found in the accessible pore volumes and the bed packing densities of the two materials. The PICA material was found to have a higher totally included and totally excluded volume than would be normally expected. The chromatographic method provides results which are more useful for the application of these materials to separation sciences.
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  • 45
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    Chromatographia 42 (1996), S. 401-404 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Hummel Dreyer method ; Sulfinpyrazone ; Bovine serum albumin ; Scatchard-Rosenthal plot
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Hummel-Dreyer method was used to study the binding of sulfinpyrazone to bovine serum albumin. The technique involves our newly developed internal calibration method with the elution pattern consisting of two positive peaks and with the integrator to evaluate the area of second peak. From the area of the second peak the numerical value ofL b (the amount of drug bound to protein) was calculated. Sctachard-Rosenthal plot was used to estimate the binding parametersn i (the number of binding sites) andk i (the binding constants). The results are compared with those obtained by equilibrium dialysis.
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  • 46
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Cu(II) dimethyldithiophosphate complex ; Malathion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A high-performance liquid chromatographic method has been developed for the quantitative determination of the organophosphorus pesticide malathion. The method is based on alkaline hydrolysis of malathion to dimthyldithiophosphate (DDTP) which is complexed with copper(II) and extracted in chlorofrom. The complex is injected onto a Hypersil ODS or Licrosorb sicolumn and eluted with acetonitrile:methanol:water (80∶10∶10 v:v:v) or chloroform. Detection is at 245 or 260 nm. A linear calibration curve was obtained for 24–240 μg ml−1 DDTP and a detection limit of 2.4–4.8 ng DDTP per injection. The method was applied to the analysis of malathion in commerical products after spraying on leaves. Extrction efficiency of malathion from leaves in acetone-water was also evlauted.
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  • 47
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Column liquid chromatography ; Pesticide residues ; Surface water analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A monitoring programme based on gas chromatography (NPD, ECD) using MSD for confirmatory purposes and coupled-column liquid chromatography was applied to the analysis of pesticide residues in surface water from a predominantly agricultural area of Spain (Comunidad Valenciana). Samples analysed by means of enzyme-linked immunosorbent assay gave similar results to those obtained by GC (MSD) for the determination of total triazines. The test employed had the advantages of a simple test procedure, short analysis time and high confirmatory value. Nevertheless, the multiresidue character, accuracy and unequivocal identification of individual pesticide residues of GC (MSD) make this technique the most appropriate for environmental monitoring programmes. In this monitoring programme about 200 samples were analysed between 1993–1994. 27 different pesticides were detected in 91 of these samples. The pesticides more frequently detected were dimethoate, methidathion, endosulfan A and B, endosulfan sulphate and pirimicarb. The highest concentrations found were 39.9 μg L−1 of dimethoate, 10.6 of pirimicarb and 10.6 of methidathion.
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  • 48
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Liquid membrane extraction ; Chlorinated phenols ; Natural water samples
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A sample preparation method has been developed for the determination of chlorinated phenols in water. The method is based on a supported liquid membrane extraction system connected on-line to liquid chromatography with electrochemical detection. The supported liquid membrane technique utilizes a porous PTFE membrane. The membrane is impregnated with an organic solvent which forms a barrier between two aqueous phases and enables selective extraction. The technique can easily be coupled in a flow system. In this investigation five chlorinated phenols (1–5 chlorine atoms) were extracted from natural water samples. Extraction for 30 minutes resulted in detection limits of approximately 25 ng L−1.
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  • 49
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Gradient elution of synthetic polymers ; Polystyrene and various styrene copolymers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Retention times in gradient liquid chromatography of synthetic polymers are often dependent on sample size. They increase with column load if the separation mechanism is governed by a solution process but decrease with increasing load if the mechanism is governed by adsorption. Since retention times independent of sample size are a prerequisite for peak identification as well as for the correct measurement of elution bands of samples with a broad distribution, measures to counteract sample-size effects deserve attention. Usually both solubility and adsorption are effective in gradient liquid chromatography of synthetic polymers. An appropriate balance of both effects is suitable for diminishing the influence of sample size on retention time of synthetic polymers. Ternary gradients allowing independent control of solubility and adsorption are promising.
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  • 50
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Supercritical fluid extraction ; Carbamate pesticides ; Soils ; Cereal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method for the supercritical fluid extraction of carbamate pesticides (propoxur, aminocarb, carbaryl and methiocarb) from soil and cereal samples using CO2 is proposed. Extractions were at 378 bar and 54 °C. Analytes were determined in the extracts by HPLC with fluorescence detection after post-column derivatization. Recoveries from spiked soil ranged between 39.6 and 91.7%, depending on analyte and soil components. Lowest recoveries were from sandy soils. Aminocarb could not be recovered from any soil using CO2. Recovery of aminocarb from diatomaceous earth was improved by adding methanol to the extraction cell prior to SFE, but the effect was not observed in soil samples. Recoveries for propoxur and aminocarb from spiked wheat were about 75%, and only between 30–50% for aminocarb from corn and oats, and carbaryl from wheat. Fat was coextracted using CO2 and retained in the trap together with the analytes, however, appropriate rinsing solvent allowed on-line clean-up of the extract.
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  • 51
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Peak overlap ; Fluorescence detection ; H-Point standard additions method ; Water analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The H-Point Standard Additions Method (HPSAM) is proposed in order to resolve overlapping peaks in liquid chromatography by using a conventional fluorescence detector. The method uses as analytical signals the heights or the areas obtained at two previously selected emission wavelengths, and good results are obtained for highly overlapping peaks with highly overlapping fluorescence spectra. The principal benefits of the method are the ease of finding the required wavelengths, its insensitivity to changes in the retention time of the peak from one injection to another, and the possibility of using it in highly or only partially overlapping peaks. We have applied the method to the determination of phenol and cresols in water, resolving by the proposed method the overlapping peaks ofm- andp-cresol.
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  • 52
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Synthesis of new liquid phases ; Evaluation of new phases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Three columns, mono-ol, butylphenyl and perfluorinated synthesized through the reaction of an olefin with a silica hydride intermediate, are evaluated for the separation of various model compounds. Two of the columns, mono-ol and perfluorinated, can operate in both the normal phase and reversed phase modes. Some effects of the hydride surface are detected, particularly for the perfluorinated phase. A four-component steroid mixture is tested on both the mono-ol and perfluorinated phases in the normal mode.
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  • 53
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Nitroaromatics ; Solid phase extraction ; Reduction and derivatization ; Fluorescence detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A selective and sensitive method for determination of nitroaromatics is described. The analytes were reduced to corresponding primary amines with iron powder and then derivatized with fluram in citrate buffer to form pyrrolinones. The highly fluorescent pyrrolinones were isolated and preconcentrated by octadecylsilane solid phase extraction cartridge followed by reversed-phase, high-performance liquid chromatographic analysis. Detection was at 395–495 nm. Various aspects such as the reduction process, derivatization, solid phase extraction and chromatographic separation were optimized. Analysis time was relatively short due to a special design for successive reduction and preconcentration. Limits of detection for 3-nitrophenol, nitrobenzene, 4 and 2-nitrotoluene were less than 60, 12, 60 and 280 ng L−1 respectively.
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  • 54
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Yoghurt ; β-Galactosidase activity ; Glucose ; Galactose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new method has been developed for the HPLC determination of the activity of lactase from the microorganisms in yoghurt. The method is based upon the ability of β-galactosidase to hydrolyze lactose bonds in glucose and galactose. To determine such activity in yoghurt, 1 mL of yoghurt was diluted 1∶10 with 0.1 M phosphate buffer (pH 7) containing 2 % (w/v) lactose and 5 mM dithioerythritol as reducing agent; the mixture was the incubated and injected into the HPLC. Lactase activity remained high as long as the number of viable microorganisms did not fall below the minimum CFU·mL−1 (107). This method is more repeatable than conventional colorimetric determination, and may also be automated for routine analysis.
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  • 55
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Micellar vs. reversed phase separation ; Thiram in river water ; Dithiocarbamate fungicides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary After a comparative study of conventional reversed phase and micellar liquid chromatography a method is described for the determination of the fungicide thiram in river water based on the use of micelles of CTAB. The method involves the extraction/concentration of thiram with a C18 cartridge followed by separation on a C18 reversed-phase column with a mobile phase of 20% (v/v) acetonitrile/0.01 M CTAB in phosphate buffer (pH-6.3), and detection at 254 nm. The method allows the determination of thiram in the presence of other water-soluble dithiocarbamate fungicides (nabam, ziram and ferbam) with a limit of detection of 36 pg mL−1 for a typical 20-fold preconcentration.
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  • 56
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    Chromatographia 43 (1996), S. 654-658 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Thin-layer chromatography ; Ion-pairing ; Sulfonamides ; NH2-Modified stationary phase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Thin-layer and column high-performance liquid chromatography based on amino propyl-modified silica gel using aqueous and non-aqueous mobile phases containing organic modifier and cationic or anionic ion-pairing reagents were used for the determination ofR F andk values of some sulfonamides. The influence of the different organic modifiers and ion-pairing reagents on retention has been compared.
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  • 57
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    Chromatographia 42 (1996), S. 595-598 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Non-porous, reversed phase packing ; Fast peptide separation ; Peptide mapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Kovasil-H, a new 1.5 μm, non-porous, silica-based, reversed phase packing was investigated for the peptide mapping of Bovin Serum Albumin (BSA) and Cytochrome c tryptic digests and for the quality control of trypsin. Using short columns (33–66 mm) and high temperature, very short analysis times and high sensitivities were attained. No special modification of commonly used liquid chromatographs are necessary for the application of this method.
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  • 58
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Caffeine ; Pharmaceutical formulations ; Micellar liquid chromatography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An HPLC procedure is described for the determination of caffeine in pharmaceutical preparations. A Spherisorb octadecylsilane ODS-2 C18 analytical column and spectrophotometric detection at 273 nm were used. The chromatographic behaviour of caffeine with different micellar eluents containing sodium dodecyl sulphate (SDS) is described. The determination of caffeine in pharmaceutical preparations was performed by use of a mobile phase containing 0.05 M sodium dodecylsulphate (SDS) and 1.5% propanol at pH7. At a 6.0 μg mL−1 concentration level the peak area and peak height repeatability were 2.6 and 2.4%, respectively. The application of the proposed method to the analysis of five pharmaceutical formulations, using peak heights as the dependent variable, gave recoveries between 85 and 104% of the values declared by the manufacturers. The proposed procedure for the determination of caffeine is rapid (15 min per sample), reliable and free from interferences.
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  • 59
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Leucovorin, methotrexate ; On-line, post-column UV irradiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An improved, reversed-phase, high-performance liquid chromatography (HPLC) method with dual UV-fluorescence detection for simultaneous determination of the antifolate methotrexate, the folate leucovorin and their two main metabolites 7-hydroxymethotrexate and 5-methyltetrahydrofolate, respectively is presented. The fluorescence intensity of leucovorin could be significantly increased by on-line, post-column irradiation with UV at 254 nm thus lowering the limit of detection for leucovorin to 0.2 ng absolute at a signal-to-noise ratio 3∶1.
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  • 60
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Carbohydrates ; Anomer separations ; Post-column derivatization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A sensitive post-column fluoresence method based on the reaction of reducing sugars with a fluorigenic reagent (benzamidine) under alkaline conditions and elevated temperature is described. Optimum reaction conditions suitable for the detection of fluorescent reaction products have been investigated. A porous graphitized carbon column (shandon Hypercarb) was employed as the chromatographic solid phase and elution was isocratic by an aqueous acetonitrile mixture. A special problem in sugar analysis is the tendendy of anomer formation giving doublet peaks. This tendency varies largely among the different sugars, and systematic studies on conditions that eliminate this problem were performed. Efficient and selective separations of a series of disaccharides were obtained using high temperatures and a low concentration of acetonitrile in the mobile phase. The detection limits (S/N=3) with an injection volume of 20 μL ranged from 10–60 picomoles. Linear calibration graphs were obtained in the 2–20 μM concentration range (r 2〉0.99). A relative standard deviation between 1–3% (n=6) demonstrated good precision of the developed system.
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  • 61
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chromogenic reagent ; Chloroformate ; Pre-column derivatization ; Amino acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The chromogenic reagent 4-phenylazobenzyloxycarbonyl chloride (PAZ-Cl) was used for the automated pre-column derivatization of amino acids (AAs) at ambient temperature followed by liquid chromatographic separation of the derivatives formed. Since in previous investigations it was realised that the selectivity of a C-18 stationary phase decreased after 40 injections of PAZ-AAs the suitability of 12 reversedphases distinguished by silica modification, carbon content, and particle characteristics was tested. Among these columns only a polymer-coated C-18 stationary phase furnished satisfactory repeatability of retention times for 250 analyses.
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  • 62
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ruthenium diimine complexes ; Inorganic synthesis ; Kinetics monitoring
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The synthesis of the complex [(bpy)2Ru(Im)2]2+ (bpy=2,2′-bipyridine; Im=imidazole) has been monitored by reversed-phase HPLC. The analytical results obtained during the reaction have shown that it is feasible to identify and isolate the [(bpy)2RuIm(H2O)]2+ complex as a reaction intermediate. The optimization of the synthetic procedures for these two species has been established and the compounds have been obtained in high purity. The use of HPLC has enabled complete analytical control of the synthesis of the [(bpy)2RuL2]2+ class of compounds, enabling the identification of reaction intermediates.
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  • 63
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Wine ; Sorbic acid ; Styrene-DVB sorbents ; Detection limit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method is proposed for the determination of sorbic acid in wines using a hydrogen sulfonated divinyl benzene-styrene copolymer (DVB-H) HPLC column and isocratic elution with 0.01N H2SO4:CH3CN (75:25). UV detection at 258 nm permits analysis by direct injection of white and red wines without significant interference between the peaks of sorbic acid and other sample components. The limit of detectability of the method is 0.01 mg L−1 with an average recovery of 99.6% and an average % RSD of 0.87. Analyses of 30 wine samples by the proposed method and the official EEC spectrophotometric method show that there is a good correlation between the results of the two methods, although the HPLC analyses are clearly more precise and accurate.
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  • 64
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Reverse-phase LC columns ; Chromatographic classification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The ever-increasing number of commercially available reversed phases with which the analyst is confronted can cause problems in column selection. These and the non-standard test procedures used by the column manufacturers and packing companies cause further confusion. In order to independently compare and contrast a range of well established C18 stationary phases, we have performed a modified column characterization approach, based on Tanaka's methodology, on thirty commonly used phases in our laboratory. These results have been evaluated and presented in various formats as Principal Component Analysis, Cluster Analysis, Tabular Format and Radar Plots in order to assist in observing similarities and differences between phases. The results indicate that, while no two phases are exactly the same (with the exception of “me-to” clones), it is possible to characterize phases into different classes based on their chromatographic performance against selected test probes. The paper illustrates the similarities and differences between these phases. The column characterization described in the paper can form the basis of a rational column selection protocol by either careful matching of the appropriate column characteristics to the analyte's physico-chemical properties or by a systematic evaluation of columns from our various categories.
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  • 65
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Oligomeric stationary phases ; Enthalpy-entropy compensation ; Methylene and phenyl selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The effect of temperature and mobile phase composition (methanol-water) on the retention behaviour of an oligomeric series of n-octylsilyl bonded phases in reversed-phase liquid chromatography has been investigated. Plots of lnk against 1/T (van't Hoff plot) and the enthalpy of transfer (ΔHo) yields linear relationships under the conditions studied. The ΔHo values of the aromatic hydrocarbons and n-alkyl benzoates are higher than those of the polar compounds due to their higher level of interaction with the stationary phase. A linear plot of ΔHo vs. ΔSo suggest that the retention process, which is essentially controlled by non-specific (dispersive) interactions between the solutes and the bonded ligands, is identical for all cases evaluated. The existence of similar retention mechanisms is confirmed by the constant value of the enthalpy-entropy compensation temperature of the columns for a given class of componds. As expected, decreasing the methanol content (% v/v) of the mobile phase results in increased eluite retention times. The methylene and phenyl selectivities are found to be independent of the carbon content of the stationary phases and varied only with the eluent composition. In addition to their high stability under aggressive mobile phase conditions as previously reported, the results of this study generally showed that the solute retention process on oligomeric phases are similar to those exhibited by the conventional reversed phases.
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  • 66
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Pharmaceutical formulations ; Triprolidine ; Pseudoephedrine ; Paracetamol ; Dextromethorphan
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple, rapid and specific HPLC method has been developed for the determination of triprolidine, pseudoephedrine, paracetamol and dextromethorphan, in combination, in different pharmaceutical dosage forms, using a reversed-phase C18 column, gradient elution, and UV detection at 254 and 280 nm. No preliminary extraction procedure is required for liquid formulations and a very simple extraction procedure is required for tablets and creams. The recovery of the drugs ranged from 96.0 to 98.7%. The assay results obtained for eight commercially available formulations were in agreement with the amounts declared. The linearity and precision of the method have been assessed.
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  • 67
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Microdialysis ; Carbamazepine ; Human serum albumin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple and rapid method for determination of the parameters of the interaction between drugs and protein, including the association constant and the number of binding sites, has been developed by use of a microdialysis sampling technique combined with high-performance liquid chromatography. The drug and protein (carbamazepine (5H-dibenz[b,f]flazepine-5-carboxamide, CBZ) and human serum albumin (HSA) were used as examples) were mixed in different molar ratios in 0.067 M potassium phosphate buffer, pH 7.4, and incubated at 37°C in a water-bath. The microdialysis probe was the used to sample the mixed CBZ-HSA solution at a perfusion rate of 1 μL min−1. The concentration of CBZ in the microdialysate was determined by reversed-phase high-performance liquid chromatography. Relative recovery (R), determined in vitro under similar conditions, was approximately 42.7%; theRSD ofR was approximately 1.85%. The estimated association constant (K) and the number of the binding sites,n, on one molecule of HSA were 1.06×104 M−1 and 0.880, respectively, which is in good agreement with the literature values determined by high-performance frontal analysis. The potential use of microdialysis is also discussed.
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  • 68
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    Chromatographia 44 (1997), S. 19-24 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Cisplatin stability ; Cisplatin metabolites ; Platinum phosphato-derivatives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Althoughcis-dichlorodiammineplatinum(II) (cisplatin or CDDP) is widely used for the treatment of several kinds of tumour, its stability and metabolism in biological fluids have not been completely elucidated. Conditions in which mobile phases of formic or phosphoric acids interact with platinum derivatives during chromatographic separation performed by high performance liquid chromatography on-line with inductively coupled plasma-mass spectrometry (ICPMS) are investigated. During chromatographic separation of CDDP the formic acid mobile phase does not interact with CDDP itself nor with its hydrolysis products. In contrast, the phosphoric acid mobile phase interacts, not with the CDDP itself, but with its hydrolysis products which are present only in an aged aqueous solution, to generate two platinum phosphato-derivatives. This study suggests that the phosphoric acid has greater affinity for the CDDP hydrated complexes than formic acid and the latter is more appropriate for the study of cisplatin behavior in aqueous and biological media.
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  • 69
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Porous graphitic carbon ; Diphosphine complexes ; Gold, rhenium, manganese organometallics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The isocratic high-performance liquid chromatography of 1,1′-bis(diphenylphosphino)ferrocene (dppf), 1,1′-bis(diphenylphosphino)ruthenocene (dppr), bis(diphenylphosphino)methane (dppm) and triphenylphosphine (PPh3)-substituted heterometallic Au-Mn or Au-Re carbonyl complexes is reported. A column packed with PGC (porous graphitic carbon) was used after preliminary experiments had shown that silica- and bonded-phase (silica-based) stationary phases were unsatisfactory for separation. The PGC column exhibited unique selectivity for the complexes studied. The mobile phases used were water-acetonitrile, dichloromethanehexane and tetrahydrofuran-hexane. The retention behaviour of the compounds was governed by the polar character and size of molecules, and influenced by metal-metal bond polarity. Separation of isomorphous structures with different metallocenyl moieties was achieved.
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  • 70
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    Chromatographia 44 (1997), S. 619-622 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Boldine in pharmaceuticals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method is proposed for extraction, separation, identification and quantitative measurement of boldine (I) in pharmaceuticals. The extraction of (I) from the matrix (syrups, tablets, extracts) was realized with aqueous ammonium chloride (0.02 M, pH=3.0 with perchloric acid) and the clean-up of the extract was performed by solid-phase extraction by means of cartridges containing a strong cation-exchange sorbent, from which (I) was eluted with aqueous ammonium chloride (1 M, pH=10.0 with ammonia). The final eluate was examined by HPLC. Chromatography was performed on a C-8 column with a gradient elution from 15:85 to 30:70 of acetonitrile-water containing 0.1 M sodium perchlorate (pH=3.0), in 20 min. A diode array detector was used at 302 nm for detection. The method gives recovery values greater than 98% and the reproducibility is within 6.0%.
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  • 71
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Vitamin B and C in tablets ; Experimental design ; Optimization of separation ; Multiple regression modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The ion-pair liquid-chromatographic separation of the water-soluble vitamins thiamine mononitrate, riboflavin phosphate, nicotinamide, pyridoxine hydrochloride, ascorbic acid, saccharin, and the dye Sunset Yellow FCF (E110) has been examined for the analysis of the compounds in effervescent tablets. A Draper-Lin small composite design was used to study the impact on the compounds' retention times and peak-widths (the response variables) of four different mobile phase variables: percentage of methanol as organic modifier, the concentrations of hexanesulfonate as ion pairing reagent and of triethanolamine as competitive base, and pH. The interactions of these variables were also studied. The proposed design enabled derivation of multiple linear regression equations to model each compound's retention time and peak-width at half-height. The statistical reliability of the regression models was established by comparing predicted and experimental values. By introducing the regression models into a spreadsheet program (Excel 5.0), retention times and peak-widths for each compound were calculated at fixed mobile phase pH. The values of all the other combinations of the three mobile phase variables were changed in increments of two units within their examined boundaries, resulting in 225 different rows. For each combination the compounds' calculated retention times and their corresponding peak-widths were sorted in increasing order and the resolution between successive peaks was calculated. The minimum effective resolution (R s min) between each pair of peaks and the maximum retention time (t R max) in each row were then selected and used to construct contour plots indicating the location of zones of mobile phase parameter combinations whereR s min〉1.5 and the analysis was rugged, and wheret R max values were minimum. Their common regions resulted in optimum chromatographic separations. Examples are shown of chromatographic separations obtained using mobile phase combinations which were the best compromise of the three criteria selected.
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  • 72
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Thermal lens spectrometric detection ; Diazotization and coupling derivatization ; Clenbuterol in urine ; N-(Naphthyl)ethylenediamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Clenbuterol has been determined in urine by solidphase extraction on a C18 cartridge, diazotization of the eluate with nitrite, coupling of the diazonium ion with 1-(naphthyl)ethylenediamine, and separation of the azo dye formed by HPLC with a C18 column and a micellar mobile phase containing 0.1 M sodium dodecyl sulphate, 12%n-butanol and 0.05 M citrate buffer, pH 3. Recoveries higher than 90% were obtained by mixing the samples with a 20% 0.2 M NaOH before extraction. Limits of detection of 51 and 6.7 ng L−1 were obtained with spectrophotometric and thermal lens spectrometric detection, respectively; respective repeatabilities were 3.1% (5 μg mL−1) and 5.6% (0.16 μg mL−1).
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  • 73
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Solid phase extraction ; Tetracycline in serum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple and rugged SPE method for the determination of tetracycline (TC), minocycline (MC) and demeclocycline (DCC) in porcine serum by high performance liquid chromatography (HPLC) was developed. The spiked serum sample was pretreated with 2% phosphoric acid followed by a simple and rugged solid-phase extraction procedure using the OasisTM HLB extraction cartridges. High and reproducible recoveries were obtained even though the cartridges were run dry. The extracted sample analytes were injected onto a Waters SymmetryShieldTM RP8 column. The mobile phase was a simple volatile solution containing 0.1% TFA, 2% methanol and 7% acetonitrile in Water. The antibiotics were detected at 350 nm. The calibration curves were linear from 2.0 to 25.0 μg mL−1 of TC and MC with DCC as the internal standard at a concentration of 25.0 μg mL−1. For six replicate analyses, the average recoveries of TC and MC from porcine serum sample fortified at the level of 2.5 μg mL−1 were 96.1% with 1.3% RSD and 101% with 0.54% RSD; at level of 0.5 μg mL−1 the average recoveries were 88% with 1.6% RSD and 97.8% with 1.4% RSD.
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  • 74
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Preparative scale separations ; Strong cation-exchange resin ; Amino acids ; Desalting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The uptake of sodium chloride, leucine and phenylalanine by a strong cation-exchange resin in the sodium form have been compared. Sodium chloride was excluded from the resin, as indicated by its parabolic upwards curved isotherm, and the corresponding desorption edge was sharpened (constant pattern). Isotherms for both amino acids constructed from a single elution experiment displayed slightly downwards curvature; the corresponding desorption edges spread in contrast to the breakthrough ones. The affinities of both amino acids for the resin were higher (from 15 to 40 %) in the presence of 1 M sodium chloride, indicating that hydrophobic interactions played a significant role in the mechanism of sorption. As expected from the isotherms, a mixture of 1 M sodium chloride, leucine and phenylalanine was separated with satisfactory recovery of both amino acids for a column loading of 10 % of the bed volume. Real mother liquors have also been separated under the same conditions.
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  • 75
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Catecholamine-related compounds ; pH optimization of mobile phase ; Amperometric detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A study was conducted for the optimization of the reversed-phase high performance liquid chromatographic separation of different types (acidic, basic, amphoteric and neutral) of catechol-related compounds by varying the pH. For pH to be used as the optimizing parameter, its effects on retention, peak width and peak shape had to be investigated. Therefore, the pH dependence of the amperometric detector response, as measured by the oxidation peak height or peak area, was taken into account.
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  • 76
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    Chromatographia 42 (1996), S. 29-33 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Gas chromatography-mass spectrometry ; 7-Cholesteryl acetate hydroperoxides (CAHPs) ; Thermal degradation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The thermal degradation products of the 7α- and 7β-cholesteryl 3β-acetate hydroperoxides obtained by thermal oxidation of cholesteryl 3β-acetate are reported and discussed. The hydroperoxides were degraded in both the vapour and condensed phases. The main components identified were 7-ketocholesteryl 3β-acetate, 7α- and 7β-hydroxycholesteryl 3β-acetates and the products generated from the loss of the hydroperoxide group and/or of acetic acid. Remarkable is the finding of the epoxy-hydroxy derivatives of cholesteryl acetate among the degradation products.
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  • 77
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    Chromatographia 42 (1996), S. 34-38 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; On-column ion complexation ; Simultaneous metal ion analysis ; Analysis of standard references
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Ion-pair, high-performance liquid chromatography has been used for the simultaneous separation of Cu(II), Fe(II) and U(VI) as their proposed, anionic [M(H2PO4)3]− and neutral complexes with tetrabutylammonium (TBA)+ as ion-pairing reagent. The concentration effect of (TBA)+, organic modifier and pH of the eluent on the separation was investigated. The UV detector response at various wavelengths has been optimized. Detection limits of Cu(II), Fe(II) and U(VI) were 12, 6 and 12 ng respectively. The method is compared with atomic absorption spectroscopy spectrophotometry for determination of metal ions in synthetic mixtures as well as in Standard Reference Materials (SRMs).
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  • 78
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Dextran-polyimine stationary phases ; Affinity ligands ; Ligand-exchange chromatography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Forming a polymer layer on the surface of siliceous materials is one of the methods for protecting the silica skeleton from dissolution in alkaline mobile phases as well as eliminating the negative influence of silanol groups on separated molecules e.g. proteins. Polysaccharides, especially their derivatives bearing amine groups, can play the role of the surface layer. This paper discusses the possibilities of preparing such a layer by cross-linking a dextran-polyimine mixture (rather than the traditionally used DEAE-dextran) deposited on the surface of the solid material. The results presented prove the utility of synthesized materials as supports for affinity ligands in high performance affinity chromatography or as supports for complexed metal ions in ligand-exchange chromatography. The properties of the sorbents with a polymer layer can be changed both by the composition of the cross-linked mixture and by chemical modification.
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  • 79
    ISSN: 1612-1112
    Keywords: Capillary electrophoresis ; Column liquid chromatography ; Cefotaxime impurities ; Cross validation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A micellar electrokinetic chromatography method is presented which permits separation of cefotaxime and its major related impurities. Separation was carried out at 15 kV, using 30 mM sodium dihydrogen phosphate adjusted to pH 7.2 with 5 M NaOH and which contained 165 mM sodium dodecylsulfate as electrolyte. Results obtained by capillary electrophoresis were in good agreement with those of high-performance liquid chromatography with respect to the level of the major known impurities, total impurity content and cefotaxime purity.
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  • 80
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    Chromatographia 42 (1996), S. 181-184 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ewe's milk ; Whey proteins ; Goat's milk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary High-pressure liquid chromatography (HPLC) was used to detect added cows' milk in goat and ewe's milk. Analysis of the whey proteins enabled detection of mixtures in proportions of less than 1%. The method does not distinguish between goat and ewe's milk.
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  • 81
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    Chromatographia 42 (1996), S. 191-198 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polymer-coated silica phase ; Polyaniline ; PAHs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The use of polyaniline as a chromatographic stationary phase has been examined. In the course of this work the column packing material was prepared by coating silica particles with polyaniline chloride. The aniline monomer was polymerised directly on the surface of the silica particles using a chemical method and was characterised using elemental analysis. A series of standard test compounds were employed for chromatographic characterization. The studies revealed information on the practical utility as well as the molecular interactions that took place on the stationary phase.
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  • 82
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    Chromatographia 42 (1996), S. 318-322 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Adenosine in blood ; Isocratic elution ; Stop-solution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Due to manifold physiological and cardioprotective actions of adenosine, the demand for a simple but accurate method to determine its concentration in plasma is increasing. The aim of this study was firstly to develop a simple isocratic method instead of the gradient elution or peak-shifting techniques used earlier and secondly to check conflicting data on the composition of “stop-solution”, added to the sample in order to prevent changes in adenosine concentration. Isocratic elution improved signal to noise ratio and concentrations of 100 μmol L−1 dipyridamole and 2.5 μmol L−1 erythro-9(2-hydroxy-3-nonyl)adenine in the blood sample effectively prevented both adenosine formation and degradation, even without the use of a 5′-ecto-nucleotidase inhibitor. Lowering the concentration of dipyridamole to 25 μmol L−1 caused more than a tenfold increase of adenosine concentration in two out of five cases and even 100 μmol L−1 dipyridamole alone is not sufficient to inhibit adenosine deaminase in blood samples.
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  • 83
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Structure-retention relationship ; Polar modifiers ; Molecular modelling ; Retention mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The mechanism of retention in HPLC using a non-polar solvent with a very low content of various polar modifiers as mobile phase and three stationary phases is studied. The results of preceding work are generalised to the role of each polar modifier. This allows quantification of the interaction between stationary phases and polar modifier. Moreover, by the introduction of physicochemical descriptors of eluents it is possible to obtain for each stationary phase a simple equation correlating retention of solutes to calculated descriptors of solutes and eluents. The mechanism of retention is discussed with these new general equations. The main qualitative result is proof of a direct link between the polar modifier and polar groups of the stationary phases, This link plays the major role in differences of retention.
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  • 84
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    Chromatographia 42 (1996), S. 499-505 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Hop bitter acids ; Supercritical fluid extraction ; On-line-1H NMR coupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A supercritical carbon dioxide hop extract has been analysed using on-line coupling of high performance liquid chromatography (HPLC) with1H nuclear magnetic resonance (NMR) spectroscopy. For the first time high quality NMR spectra of the six major hop bitter acids were recorded by employing the stopped-flow detection mode. The resolution of the spectra obtained is similar to that of conventionally recorded spectra. All data are in agreement with the known structures.
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  • 85
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chelation ion chromatography ; Dye impregnated resins ; Trace metals in seawater
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary High-performance chelation ion chromatography (HPCIC) involving the use of chelating dye impregnated resins has been investigated for its ability to preconcentrate and separate a range of metals in a variety of complex samples. The parameters involved in the production of dye impregnated chelating columns have been identified and investigated. A number of selected chelating dyes have been impregnated into high-performance substrates, producing a range of chelating columns, exhibiting unique retention characteristics, dependent upon the nature of the impregnated chelating ligand. These columns have been classified in terms of retention characteristics, separation efficiency, dye loading and column capacity. A brief application of the above technique to the determination of Al (III) in seawater is illustrated.
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  • 86
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chiral stationary phases ; Bonded cyclodextrins ; Reversed and normal mode separations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary β-cyclodextrin chiral stationary phases (CD-CSP) having different spacer lengths have been prepared and evaluated (retention, selectivity, resolution) for the liquid chromatographic separation of several series of enantiomers. The influence on the separations of the spacer length is discussed. The CD-CSPs were evaluated under normal and reversed mode conditions and the results compared with those from two commercial stationary phases containing β-cyclodextrin Chiradex and Cyclobond I.
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  • 87
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    Chromatographia 43 (1996), S. 5-9 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Thin-layer chromatography ; Bioactivity detection ; Bioluminescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Because luminescent microorganisms change their light emission in the presence of bioactive substances, they provide an effective way of monitoring toxicity. Here we report the direct coupling of bioluminescence to chromatography which is capable of detecting single toxic components in complex mixtures. Two approaches were investigated, utilizing thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). The TLC-bioluminescence imaging technique was developed into a versatile and rugged method and proved to be superior to the HPLC-based design. Employing genetically engineered luminescent bacteria gives customized selectivity of bioactivity detection. The combination of analytical separation technology with the biospecific sensing ability of living cells provides a novel screening tool for targeting bioactive components in complex samples.
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  • 88
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    Chromatographia 43 (1996), S. 76-78 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Rhodamine B in cosmetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method is proposed for the extraction, separation, identification and quantitative measurement of rhodamine B in cosmetics samples The colour is extracted with a solution of orthophosphoric acid in either water or DMF (depending on the type of cosmetic) adsorbed on a polyamide column, and then eluted with water and methanol. Further clean-up of the extract is performed by means of a Bond Elut C-18 cartridge, from which rhodamine B is eluted with methanol-water (8∶2). The final eluate is examined by HPLC. Chromatography is performed on a C-18 column with a gradient elution from 50∶50 to 70∶30 of acetonitrile-water, containing 0.1 M sodium perchlorate, in 15 min. A diodearray detector enables peak purity analysis. The method gives recovery values of approximately 90%, or better, and the reproducibility is within 4%.
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  • 89
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Anion-exchange chromatography ; Benzhydrylamine resin ; pK a
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary For better evaluation of the potential of benzhydrylamine resin (BHAR), used as a solid support for peptide synthesis, as a novel anion-exchange resin, the pK a of its amine group was estimated by microscopic measurement of the sizes of the dry and swollen beads. Using the volume of the bead occupied by the solvent (as a percentage) as the swelling parameter, a plot of the degree of swelling of BHAR loaded with 2.4 mmol g−1 amine groups against the pH of the medium produced a decreasing sigmoidal-type curve with increasing pH. By considering the point of inflection of the curve, a pK a value of approximately 7.5 was estimated for the amine group of the BHAR. The same approach was also applied to the lysyl derivative of the BHAR (Lys-BHAR) and pK a values around 6.5 and 10.0 were obtained for the α and ε amine groups, respectively.
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  • 90
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Diode array detection ; Explosives residues ; Nitro-compounds ; Ground water ; Ammunition waste
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An HPLC method with diode array detection for the determination of acidic aromatic nitro compounds (in particular nitrophenols and nitrobenzoic acids) in ground water around former ammunition plants is presented. The use of an isocratic mobile phase, buffered to a pH of 2.30 on a reversed phase column, allows the separation of several nitrophenols and nitrobenzoic acids, some of which are known as phototransformation products of 2,4,6-trinitrotoluene (TNT). In a ground water sample from the former ammunition site at Elsnig (Saxony, Germany) 2,4- and 3,5-dinitrophenol (18), picric acid (8) and 2,4-dinitrobenzoic acid (3) were identified in addition to a variety of explosives determined previously. The presence of these compounds was corroborated by a diode-array (DAD)-library search.
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  • 91
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Hexamethyldisiloxane ; Mobile phase component ; Silica column
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Hexamethyldisiloxane (HMDX) has been evaluated as a modifier solvent for the normal phase separation of substituted naphthalene componds as well as aromatics such as nitrobenzene, acetophenone, benzonitrile, and aniline. It is found to be a weaker eluting solvent than n-butyl ether and other commonly used normal phase solvents filling a niche in the eluotropic series. HMDX exhibited an unusual retention factor (k′) profile as a function of mobile phase composition in hexane. In a range from 0 to 40 %, thek′ values remained quite constant with increasing HMDX composition. As the concentration of HMDX progressed to 100 %, thek′ values actually increased in a generally linear fashion. This trend ink′ is due to longer solute retention not just a change in the retention time of the unretained component. Although slight silanization of the silica column may occur with initial use of HMDX, retention of these analytes on a commerical C-1 silica column is much lower with no positivek′ slope with increasing HMDX. The chromatographic data provide evidence that HMDX is likely adsorbed to the silica surface and a solute partitioning mechanism may be operative.
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  • 92
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Tandem mass spectrometry ; Fumonisin in corn products ; Electrospray-ionization (ESI) ; Selected rection monitoring (SRM)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new method has been developed for qualitative and quantitative analysis of fumonisin FB1 and FB2 in corn and corn products. After extractive sample preparation followed by solid phase extraction using a strong anionexchanger, highest selectivity and sensitivity was achieved by high-performance liquid chromatography-electrospray-ionization, tandem mass spectrometry (HPLC-ESI-MS-MS) analysis combined with selected reaction monitoring (SRM). With deuterated fumonisin FB1-d6 as internal standard the routine quantitation limit for FB1 was set at 400 pg (0.8 ng g−1 sample) with a signal-to-noise ratio of 10∶1. Almost all corn grit and corn meal samples under study were found to be contaminated with fumonisin FB1 and FB2 in concentrations ranging from 1 to 200 ng g−1. Lower fumonisin levels were found in cornflakes, popcorn and baby food, while no fumonisins were detected in canned sweet corn.
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  • 93
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    Chromatographia 43 (1996), S. 265-270 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Diode array detection ; Solid-phase extraction (SPE) ; Pesticide analysis ; Multiresidue methods ; Green bean samples
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A reversed-phase high performance liquid chromatographic (HPLC) method with an acetonitrile-methanol-water mobile phase gradient and photodiode-array detection (DAD) is described for simultaneous determination of 21 pesticides, frequently used in agriculture, of different types, namely organophosphorus, organochlorine,N-methylcarbamates, triazines and phenylureas in vegetable samples. The pesticides were extracted with acetone and then partitioned from the vegetable sample with dichloromethane. Sample clean-up was accomplished by solid-phase extraction (SPE) using both C18 and florisil SPE columns. Average recoveries from green beans ranged from 70.0 to 110.1%. Detection limits of less than 0.1 mg kg−1 were obtained.
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  • 94
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Column liquid chromatography ; ECD, UV and MS detection ; EPA Method 515.1 ; Chlorinated acidic pesticides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A comparison of the official EPA method 515.1 for determination of chlorinated acidic pesticides and a modification of it is illustrated. Extraction of the analytes from water and their determination and quantitation is by gas chromatography-electron capture detection (GC-ECD), liquid chromatography-UV detection and liquid chromatography-particle beam mass spectrometry. Although HPLC-PBMS was found to be less sensitive than the GC-ECD method, it was, nevertheless, more sensitive than HPLC-UV. The modified method is simpler, quicker and allows more accurate determination of pesticides in aqueous samples.
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  • 95
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Kelp ; Microwave hydrolysis ; precolumn derivatization ; Phenylisothiocyanate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A reversed phase high performance liquid chromatographic (RP-HPLC) method for the analysis of amino acids in kelp, using precolumn derivatization, is described. Phenylisothiocyanate (PITC) was used as the reagent for derivatization. The kelp samples were prepared by microwave hydrolysis in only 5 min; seventeen PTC amino acids were separated after hydrolysis and derivatization within 12 min. The coefficients of variation were 〉1.94 and the correlation coefficients for concentration versus response were 〉0.999 for all derivatives. The ratio of branched amino acid (BAA) to aromatic amino acid (AAA) was also studied. The method has the advantage of shorter hydrolysis and analysis times with optimum separation. In addition, it gives high repeatability of retention times and peak areas for all the amino acids present.
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  • 96
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    Chromatographia 43 (1996), S. 436-438 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Diol columns ; Optimisation ; Ephedrine ; Synopen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The effect of simultaneous variation of buffer pH, molarity and organic modifier concentration when Diol stationary phase is used was experimentally studied. An equation has been derived for the retention time in the interpolation region of ephedrine and synopen—principal active components in an antihistamine formulation.
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  • 97
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion chromatography ; Indirect detection ; Binary eluent
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Inorganic cations and anions were separated simultaneously using sodium sulfosalicylic-EDTA binary eluent on a strong basic anion-exchange column. The effects of eluent pH, concentration and complexing effect of EDTA on retention behaviour of the ions were studied. The results showed that the larger the cation, the longer the retention time — except for Ca2+.
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  • 98
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Rhenium bipyridine complexes ; Phosphorus ligand ; Inorganicity/organicity ratio ; Retention behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The high-performance liquid chromatography of fourteen rhenium complexes with phosphorus and 2,2′-bipyridine-derivative ligands has been examined. Good separation between these complexes was achieved by use of an ODS column with a 60∶40 (v/v) mixture of MeOH and KH2PO4-NaOH buffer as mobile phase. Linear correlations were observed between the capacity factors of the mono-phosphorus complexes and Fujita's organicity/inorganicity ratios for the phosphorus ligands, revealing that Fujita's organicity/inorganicity parameters are useful for evaluating of the retention behavior of these complexes.
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  • 99
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Urine clean-up ; Arsenic speciation ; Microwave assisted oxidation ; Atomic absorption spectrometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An effective clean-up method based on the precipitation of most high molecular mass inorganic salts and organic compounds in ethanol at −15°C has been developed for the determination of arsenite, arsenate, monomethylarsonate (MMA), dimethylarsinate (DMA), arsenobetaine (AsB) and arsenocholine (AsC) in urine. Analyte recovery was close to 100%. The six species were separated on an anionic HPLC column and determined by microwave-assisted oxidation-hydride generation-atomic absorption spectrometry. The detection limits and relative standard deviation of the whole procedure were within the 8–15 μg L−1 and 2.5–5.3% ranges, respectively, which allows application to the analysis of urine of people exposed to arsenic.
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  • 100
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Enantioseparation ; Chiralcel OD ; γ-Lactams
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A high-performance liquid chromatographic method is reported for the resolution of the enantiomers of a series of fused γ-lactams (2,7-diaza-3-oxo[3.3.0]octan-6-ones) with probable anti-HIV and anticancer activity. Resolution was achieved on a Chiralcel® OD column, cellulose tris-(3,5-dimethylphenyl carbamate) adsorbed on macroporous silica gel; mixtures ofn-hexane and isopropyl alcohol in different proportions were used as the mobile phase. The analysis was studied at different temperatures.
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