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  • Books  (1)
  • Articles  (3,975)
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  • Books  (1)
  • Articles  (3,975)
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  • 201
    Electronic Resource
    Electronic Resource
    Development of an Ion-pair HPLC method for the determination of 2,4- and 2,6-toluendiamine in human plasma (1998)
    Springer
    Chromatographia 47 (1998), S. 84-88 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-pair LC ; Plasma ; 2,4-Toluendiamine ; 2,6-Toluendiamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An ion-pair HPLC method is presented for the determination in plasma of 2,4- and 2,6-toluendiamine (TDA), known carcinogens. The chromatographic conditions consisted in isocratic elution on a reversed phase C18 column with 5 mM octanesulfonic acid in methanol-water, 45∶55, as mobile phase. UV detection was performed at 235 nm. Samples were analyzed after a simple single step liquid-liquid extraction and the method was validated by measurement of precision (interassay and intraassay), sensitivity, specificity, linearity, and recovery. The detection limit for both TDAs in plasma was 20 ng mL−1. The correlation coefficients based on the intrassay calibration curve were 0.998 and 0.997 for 2,6- and 2,4-TDA, respectively. The intraassay accuracy, expressed in terms of recovery, was found to be up to 89.91% and 97.05% for 2,6- and 2,4-TDA, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02466791
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  • 202
    Electronic Resource
    Electronic Resource
    Direct resolution of a new antifungal agent, voriconazole (UK-109,496) and its potential impurities, by use of coupled achiral-chiral high-performance liquid chromatography (1998)
    Springer
    Chromatographia 47 (1998), S. 649-654 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Enantiomer separation ; Voriconazole (UK-109,496) ; Effect of organic mobile-phase modifier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Coupled achiral-chiral high-performance liquid chromatography (HPLC) with an achiral amino-based column coupled with a chiral amylose-based column has been used for qualitative and quantitative determination of the potential chiral and achiral impurities of Voriconazole (UK-109,496), a new antifungal agent with two stereogenic centres. The effect of the organic mobile-phase modifier, ethanol, was studied. The assay response was linearly dependent on concentration over the range 1.2–40.4 μg for Voriconazole and 2.5–104.0 ng for the impurities. The limit of detection was 2.5 ng for each analyte.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467448
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  • 203
    Electronic Resource
    Electronic Resource
    Separation of inorganic anions and cations on titania by use of acetic acid-sodium acetate and bicine-sodium hydroxide buffers (1998)
    Springer
    Chromatographia 47 (1998), S. 655-658 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion chromatography ; Titania packings ; Inorganic anions and cations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The ion-exchange retention behavior of titania synthesized in our laboratory was investigated by ion chromatography of inorganic anions and cations. Dilute acetic acid-sodium acetate and bicine-sodium hydroxide buffers were used as mobile phases with no use of suppresor. We observed that the titania, although poor at separating monovalent anions expcept nitrite ion in this experiment, was both an anion and a cation exchanger, and selectively retained fluoride and carbonate ions. We concluded that because of its specific retention properties there were possibilites of using this amphoteric exchanger for simultaneous analysis of anions and cations, and of using it as a selective packing material for ion chromatography.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467449
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  • 204
    Electronic Resource
    Electronic Resource
    Retention behavior of morphine and its metabolites on a porous graphitic carbon column (1998)
    Springer
    Chromatographia 47 (1998), S. 667-672 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Porous graphitic carbon ; Optimization ; Morphine and metabolites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The chromatographic behaviour of a series of morphine-based opiates has been investigated using a porous graphitic carbon packing material at acid and alkaline pH. The effects of mobile phase pH, mobile phase organic percentage, column temperature and ionpairing agents were studied. All six opiates were separated within a close retention window despite large differences in measured lipophilicities of the individual opiates. The retention order was not related to the log P values of the opiates and strong retention of the fully ionised compounds was observed, particularly those with acidic functional groups. The effect of pH on the retention of the compounds indicated that the degree of ionisation of the individual compounds was important in the separation mechanism, suggesting that hydrophobic interactions were present in addition to the polar retentive effects observed above. The strong retention of the ionised glucuronide and sulphate conjugates of morphine is a particularly useful feature of the porous graphitic carbon packing material which has general applicability to the analysis of polar or ionised drug metabolites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467451
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  • 205
    Electronic Resource
    Electronic Resource
    Determination of clozapine in human plasma by solid-phase extraction and liquid chromatography with amperometric detection (1998)
    Springer
    Chromatographia 47 (1998), S. 8-12 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Amperometric detection ; Solid-phase extraction ; Plasma ; Clozapine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A sensitive and selective high-performance liquid chromatographic method has been developed for monitoring clozapine levels in human plasma. Chromatography was performed on a reversed-phase column (C8, 150 mm×4.6 mm i.d., 5 μm) with acetonitrile-aqueous sodium acetate solution, 88∶12 (v/v), as mobile phase; the flow rate was 1 mL min−1. Clozapine oxidation at +800 mV was detected amperometrically. Response was linearly dependent on concentration over the range 50–1500 ng mL−1 clozapine in plasma. Sample preparation by solid-phase extraction before HPLC analysis gave high extraction yield (94%). The accuracy and precision of the method were both very good (recovery: 97%;RSD〈3.3%).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02466779
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  • 206
    Electronic Resource
    Electronic Resource
    Characterization of the precolumn bio trap 500 C18 for direct injection of plasma samples in a column-switching system (1998)
    Springer
    Chromatographia 47 (1998), S. 299-304 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Plasma samples ; Direct injection ; Restricted-access media ; Column-switching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new restricted access media (RAM) type of precolumn, Bio Trap 500 C18, for direct injection of plasma samples in column-switching systems was evaluated with respect to the elution of plasma proteins in different mobile phases, the loading capacity of plasma samples, the chromatographic behavior during plasma injections and protein contamination of the packing and sealings. More than 95% of plasma proteins could be excluded from the precolumn within three minutes for all selected mobile phases. Quantitative analyte recoveries could be obtained by injecting plasma samples ranging from 5 to 500 μL with the analyte mass〉150 ng onto a BioTrap 500 C18 column (20×4 mm I.D.). One precolumn tolerated about 15 mL of plasma injection without out noticeable change in retention and pressure. Clogging of the precolumn was encountered (≥45 mL of plasma) due mainly to the adsorption of proteins on the packing. The performance of the analytical column (Kromasil C18) was also examined. The column efficiency decreased by 60% after processing 45 mL plasma in total.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02466535
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  • 207
    Electronic Resource
    Electronic Resource
    Characterisation of pitch by HPLC (1998)
    Springer
    Chromatographia 47 (1998), S. 373-382 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polyaromatic hydrocarbons ; Pitch
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new high performance liquid chromatography method for the characterisation of toluene-soluble fractions of pitches has been developed. Although a chromatographic system typical of size exclusion chromatography was used, results indicate that, for these structurally complex samples, separation does not follow the usual discrimination by molecular size. A differentiation between several classes of polyaromatic hydrocarbons is achieved instead. Data are reported on the analysis of individual standard polyaromatic hydrocarbons, showing that four different elution ranges can be observed: three ofcata-condensed compounds (Cata1, Cata2 and Cata3) and one ofperi-condensed compounds (Peri). Results are reported proving the capacity of this high performance liquid chromatography method to distinguish between pitches of different origin and nature. It is also effective for the study of the chemical reactions occurring during heat treatment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02466467
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  • 208
    Electronic Resource
    Electronic Resource
    Determination of the five major opium alkaloids by reversed-phase high-performance liquid chromatography on a base-deactivated stationary phase (1998)
    Springer
    Chromatographia 47 (1998), S. 21-24 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Opium alkaloids ; Papaver somniferum L.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A reversed phase HPLC method for the separation of the five major alkaloids fromPapaver somniferum L., morphine, codeine, thebaine, papaverine and noscapine, has been developed and validated. By use of a basedeactivated silica-based stationary phase excellent peak shape was achieved for each substance. The five alkaloids were quantified by internal standardization within 20 min and with good precision. The method is applicable to opium and to poppy straw.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02466781
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  • 209
    Electronic Resource
    Electronic Resource
    On-line extraction and determination of carbofuran in raw milk by direct HPLC injection on an ISRP column (1998)
    Springer
    Chromatographia 47 (1998), S. 81-83 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Carbofuran pesticides ; On-line analysis of milk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method has been developed for extraction and determination of carbofuran in milk. The method involved direct injection of raw milk on to a human serum albumin dimethyloctyl-silica gel (HSA-C8) column and the use of 80:20 (v/v) 0.01 M phosphate buffer pH 5.5-acetonitrile as mobile phase. UV spectrophotometric detection was performed at 220 nm. Identification was based on retention time. Quantification was performed by automatic peak-area determination and was calibrated by use of an external standard.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02466790
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  • 210
    Electronic Resource
    Electronic Resource
    High-Performance liquid chromatographic determination of dibromomannitol in plasma (1998)
    Springer
    Chromatographia 48 (1998), S. 17-19 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Dibromomannitol in plasma ; Pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Myelobromol 1,6-dibromo-1,6-dideoxy-D-mannitol (dibromomannitol, DBM) is a bifunctional alkylating agent that has been in clinical use since 1963. It is currently included at high dose in preconditioning regimen for bone marrow transplantation (BMT) and is a main-stay of treatment for polycythaemia vera. A high-performance liquid chromatographic method was developed for the determination of DBM in the plasma. The basis of the assay is a derivatization with sodium-diethyldithiocarbamate at 42°C in the presence of 1-bromo-1-deoxy-3,6-anhydro-galactitol as internal standard (IS). The analysis was carried out on a 250×4mm Hypersil 5 CPS column equipped with a 20×4 mm Hypersil 10 CPS precolumn. The eluent consisted of heptane:isopropyl-alcohol: glacial acetic acid=600:76:80 w/w. The flow rate was 1.2 mL min−1. UV detection was performed at 254 nm. The calibration graph was linear in the concentration range of 2.5–260 μM of DBM in plasma. The limit of detection was 1.0 μM. The precision and accuracy of the method was between the good laboratory practice (GLP) required limits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467509
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  • 211
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    Electronic Resource
    Monitoring of biologically active amines in cereals and cereal based food products by HPLC (1998)
    Springer
    Chromatographia 48 (1998), S. 37-42 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Biologically active amines ; Polyamines ; Cereal and Cereal products
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Biologically active amines (putreanine sulphate, N-acetyl putrescine, putrescine, cadaverine, histamine, agmatine, N-acetyl spermidine, spermidine, spermine) were separated and quantified in cereal flour and cereal products by a liquid chromatographic method. The method consists of the separation of ion pairs formed between biologically active amines and octanesulphonic acid on a reversed-phase column, postcolumn derivatization with o-phtalaldehyde-2-mercapthoethanol and spectrofluorometric detection. Results of the reliability study were satisfactory. The method was linear for each amine at 1–10 mg L−1. Putrescine and spermidine were the only amines always detected in cereal flour and cereal products, ranging from 2.45 to 47.83 mg kg−1 for putrescine and 3.27 to 37.14 mg kg−1 for spermidine. The most important differences among types of samples were found in polyamine derivatives.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467513
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  • 212
    Electronic Resource
    Electronic Resource
    Comparative study on determination of fumagillin in fish by normal and reversed phase chromatography (1998)
    Springer
    Chromatographia 48 (1998), S. 48-52 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Normal- and reversed-phase LC ; Fumagillin in fish samples
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Fumagillin is an antibiotic agent mostly used in the veterinary profession. A normal-phase liquid chromatographic method was developed for the determination of this drug in fish matrices. A hexane-dichloromethanedioxan-2-PrOH-acetic acid (43:43:9:5:0.1 v/v %) eluent was used on a Perkin Elmer silica gel column. For validation of the process a reversed-phase HPLC method was also developed (eluent: acetonitrile-water-bicyclohyxylamine 70:30:0.05 v/v %, with Spherisorb ODS, as stationary phase). Recovery is about 100% and the limit of detection is 5 ng g−1 for meat samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467515
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  • 213
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    HPLC separation of hydrogenated derivatives of buckminsterfullerene (1998)
    Springer
    Chromatographia 48 (1998), S. 59-64 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Buckminsterfullerene ; Hydrogenation ; Separation technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The effect of composition and flow rate of the mobile phase on the HPLC separation of hydrogenated buckminsterfullerene (C60Hn n=2–38) was investigated on BuckySep column. Toluene was used as the basic solvent and hexane, heptane, cyclohexane, THF, acetonitrile, acetone, ethanol and 2-propanol as co-solvents. The fraction of co-solvents was varied 10–80%, and the flow rate 1–0.1 mL min−1. Toluene-acetonitrile 65∶35 and toluene-acetone 50∶50 provided the best separation. Under the best conditions complete separation of C60H2 and almost complete separation of the four most abundant isomers of C60H4 were achieved. Separation of derivatives with higher hydrogen content was very poor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467517
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  • 214
    Electronic Resource
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    The preparative chromatographic enantioseparation of a racemic morphanthridine analog on a chiral stationary phase (1998)
    Springer
    Chromatographia 47 (1998), S. 440-442 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Preparative scale separations ; Chiral stationary phase ; Enantiomer separation ; Morphanthridine analog
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The preparative chromatographic enantioseparation of a chiral morphoanthridine analog has been performed on an analytical column using amylose-tris(3,5-dimethylphenylcarbamate) as chiral stationary phase. The racemate (100 mg) was resolved to baseline within 15 min. This paper describes the development of the method, estimation of the capacity of the chiral stationary phase and discussed the potential of the chromatography if performed under preparative conditions. From the results and calculations presented it seems likely that the resolution of 70 tons year−1 could easily be achieved on 30 kg of stationary phase with a mobile-phase consumption of only 720 L day−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02466476
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  • 215
    Electronic Resource
    Electronic Resource
    An improved extraction of marrubiim fromMarrubium vulgare (1998)
    Springer
    Chromatographia 47 (1998), S. 449-450 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chitin stationary phase ; Marrubiin ; Analgesic activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Marrubiin is the main active compound isolated fromM. vulgare, a medicinal plant used in folk medicine to cure several diseases. The present study shows that chitin, an abundant natural polymer, may be successfully in chromatography column to separate marrubiin from complex mixtures. The experimental procedure described here represents an efficient and rapid method to obtain such compound in high yield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02466478
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  • 216
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    Applications of molecularly imprinted materials as selective adsorbents: Emphasis on enzymatic equilibrium shifting and library screening (1998)
    Springer
    Chromatographia 47 (1998), S. 465-469 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Affinity chromatography ; Molecular imprinting ; Molecular recognition ; Combinatorial libraries
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Molecular imprinting is an attractive method for producing highly selective adsorbents, and several new and potentially useful applications based on molecularly imprinted polymers (MIPs) have been described in recent years. In this article, we highlight some of the areas where these materials have found application, and also describe some new fields of application where the selectivities of imprinted materials can be gainfully employed, for example as binding matrices in the screening of combinatorial libraries, and as auxiliary agents in enzymatic syntheses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02466482
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  • 217
    Electronic Resource
    Electronic Resource
    On-line monitoring of monosaccharides and ethanol during a fermentation by microdialysis sampling, liquid chromatography and two amperometric biosensors (1998)
    Springer
    Chromatographia 47 (1998), S. 501-508 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Fermentation ; Microdialysis sampling ; Monosaccharides and ethanol ; On-line monitoring ; Biosensors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Two amperometric biosensors were used as detection units in liquid chromatography for on-line monitoring of the production of fuel ethanol during a fermentation. Sampling was performed with a microdialysis probe, and the dialysate was introduced into a liquid chromatographic system providing separation of the substrates and the product: three monosaccharides and ethanol. The analytes were detected by two carbon paste electrodes based on pyranose oxidase and alcohol oxidase, respectively, co-immobilised with horseradish peroxidase, operating in parallel at −50 mVvs. Ag/AgCl. The measured linear ranges of the biosensors by direct injection into the LC system were for glucose 0.3–2.5 g L−1, xylose 0.5–6.7 g L−1, galactose 0.5–6.7 g L−1, and ethanol 1.6–11.7 g L−1, respectively. Injection of standard solutions were required to monitor the stability of the biosensors. Due to the strict selectivity of the biosensors, no interference from other compounds in the broth was encountered from other compounds in the broth was encountered in the quantification. The fermentation process was monitored for 16 h. The on-line results were compared with off-line measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467486
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  • 218
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    Determination of cisapride in human plasma by high-performance liquid chromatography (1998)
    Springer
    Chromatographia 47 (1998), S. 537-541 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Cisapride in plasma ; Pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An HPLC method has been developed for the quantification of cisapride in plasma for pharmacokinetic studies. Clebopride was used as internal standard. Plasma samples were extracted at alkaline pH withtert-butyl methyl ether. The organic phase was then extracted with sulphuric acid to eliminate endogenous interferences, and cisapride and the internal standard were then extracted at alkaline pH intotert-butyl methyl ether. After evaporation oftert-butyl methyl ether, the residue was analysed by HPLC. Chromatography was performed at 20°C on a 250mm×4mm i.d. reversed-phase column selective for basic compounds. The isocratic mobile phase was 48∶52 (v/v) acetonitrile-water containing 0.05 M potassium dihydrogen phosphate and 0.04 M triethylamine, adjusted to pH 5.5; the flow rate was 1 mL min−1. Cisapride and the internal standard were detected by ultraviolet monitoring at 276 nm. The calibration graph was linear for quantities of cisapride from 1 to 200 ng mL−1. Intra- and inter-day precision (CV) did not exceed 13.98%. The limit of quantitation (LOQ) was 0.68 ng mL−1 for human plasma. The applicability of the method has been demonstrated in a pharmacokinetic study of normal volunteers who received 10 mg cisapride orally.
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    URL: http://dx.doi.org/10.1007/BF02467491
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  • 219
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    Enantiomeric separation of four methylenedioxylated amphetamines on β-cyclodextrin chiral stationary phases (1998)
    Springer
    Chromatographia 47 (1998), S. 285-290 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Enantiomeric separation ; β-Cyclodextrins ; Methylenedioxylated amphetamines ; Ecstasy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Native and derivatized β-cyclodextrins such as chiral stationary phases (CSP) were used for the simultaneous enantiomeric separation of four methylenedioxylated amphetamines (MDA, MDMA, MDEA and MBDB) by liquid chromatography. Fluorimetric detection was used in order to enhance sensitivity and selectivity. The mobile phase was, optimised by studying the influence of pH, triethylamine concentration, organic solvent type, column temperature and flow rate of the mobile phase. This method was validated by determining linearity, precision, accuracy, limits of detection and quantification, and was applied to the stereoselective analysis of illicit tablets (23 samples) and of human whole blood samples (spiked samples and two post-mortem cases). Whereas no significant deviation from a racemic ratio was observed in the tablets contents, the analysis of blood samples showed an enantioselective metabolism of MDMA.
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    URL: http://dx.doi.org/10.1007/BF02466533
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  • 220
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    Aminopropyl-silica as an advantageous alternative to nonpolar sorbents for continuous cleanup/preconcentration of vitamin D3 metabolites (1998)
    Springer
    Chromatographia 47 (1998), S. 367-372 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Aminopropyl-silica sorbent ; Continuous cleanup/preconcentration ; Hydroxyvitamin D3 metabolites ; Flow injection analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new procedure for continuous cleanup and concentration of hydroxyvitamin D3 metabolites prior to their separation by HPLC and UV-detection is reported. The process is based on the use of aminopropyl-silica as solid-phase sorbent as an alternative to the use of nonpolar sorbents. The improvement thus achieved has been tested by comparing the results with those obtained using octadecyl-C18 as non-polar sorbent. The comparison has been based on the calibration graphs (linear range, detection and quantitation limits), precision and multiple standard addition method.
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    URL: http://dx.doi.org/10.1007/BF02466466
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  • 221
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    Simultaneous determination of 3,4-dihydroxymandelic acid, 4-hydroxy-3-methoxymandelic acid, 3,4-dihydroxyphenylglycol, 4-hydroxy-3-methoxyphenylglycol, and their precursors, in human urine by HPLC with electrochemical detection (1998)
    Springer
    Chromatographia 47 (1998), S. 396-400 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Coulometric detection ; Mandelic acids ; Phenylglycols ; Urine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method has been developed for the quantification of urinary 3,4-dihydroxymandelic acid (DOMA), 4-hydroxy-3-methoxymandelic acid (VMA), 3,4-dihydroxyphenylglycol (DHPG), and 4-hydroxy-3-methoxyphenyglycol (MHPG). Separation and determination of these compounds in biological samples was previously thought to be very difficult. In this work the separation has been achieved by reversed-phase high-performance liquid chromatography with step-wise gradient elution with three mobile phases. The conditions for coulometric detection have been optimized for effective determination of these compounds. In analysis of a sample of human urine, after a simple deproteinization proceudre, DOMA, VMA, DHPG, and MHPG were separated from interferences and quantified successfully; the average levels of these compounds in six different samples were 33.87±1.03, 1202±41.3, 31.3±1.92, and 80.6±2.15 μg (24 h)−1, respectively. Their precursors E, MN, DOPA, DA, NE, DOPAC, HVA, 3MT, and NMN, and the indolamine 5HT and its metabolite 5HIAA (a list of abbreviations is given at the end of the paper) can also be determined simultaneously in the same chromatographic run. The overlapping peak of DHPG was resolved by deconvolution.
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    URL: http://dx.doi.org/10.1007/BF02466470
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    Optimization of solvent selectivity for the chromatographic separation of fat-soluble vitamins using a mixture-design statistical technique (1998)
    Springer
    Chromatographia 47 (1998), S. 401-412 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Optimization ; Mixture design ; Special cubic polynomial model ; Pareto-optimality ; Overlapping resolution mapping (ORM)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A systematic approach, using a mixture-design statistical technique, has been developed for selecting the optimum mobile phase for the separation of fat-soluble vitamins in reversed-phase high-performance liquid chromatography. A quaternary mixture of methanol, acetonitrile, tetrahydrofuran and water was used as mobile phase. Retention time and peak width were recorded in ten runs augmented with five replicates and the data were subsequently fitted to special cubic polynomial models. The resulting mathematical equations enabled prediction of resolution over the entire parameter space. Contour plots of minimum effective resolution and maximum retention time as a function of mobile phase composition are presented and discussed. Visual inspection of these plots provides an overview of the quality of the separation and the analysis time required for each possible mobile-phase composition with n the parameter space. It is demonstrated that the methodology followed was an important tool which enabled the taking of informed decisions necessary for selection of the optimum mobile phase for a chromatographic separation. A combination ofR S minimum andt R maximum as optimization criteria in a multicriteria decision-making plot using pareto-optimality concept is discussed. This combination enabled visual demonstration of the compromise between separation quality and the economics of analysis time. Our methodology has been compared with the common used technique of ‘overlapping resolution mapping’.
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    Predicting the selectivity of imprinted polymers (1998)
    Springer
    Chromatographia 47 (1998), S. 457-464 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Imprinted polymer ; Non-covalent imprinting ; Selectivity and capacity ; Association constant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Imprinted polymers as stationary phases for HPLC separations have been the subject of extensive investigations in recent years. In order to aid the rational design of synthetic protocols for the preparation of imprinted polymers, a series of calculations were made to assess the equilibrium concentration of templatemonomer complexes as a function of association constant (K) for the functional groups involved in the interactions and initial concentrations of reactants. This data was then used to predict the selectivity of polymers prepared under different reaction conditions and the model was tested using an experimentally determined value ofK and separation factors taken from the literature.
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    Chiral discrimination ofN-(dansyl)-dl-amino acids on human serum albumin stationary phase: Effect of a mobile phase modifier (1998)
    Springer
    Chromatographia 48 (1998), S. 431-435 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; N-(dansyl)-dl-amino acids ; Human serum albumin ; Chiral discrimination ; Optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The effect of perchlorate anion as mobile phase modifier on the separation factor, α, forN-(dansyl)-dl-norvaline andN-(dansyl)-dl-tryptophan on a human serum albumin (HSA) column was studied by varying the concentration,c, of the chaotropic agent and the column temperatureT. Gibbs-Helmholtz parameters Δ(ΔH) and Δ(ΔS) between thed andl enantiomers were determined from linear van't Hoff plots of lnα against 1/T. Thermodynamic results indicated that the enhancement of the separation factor observed asc was increased was enthalpically controlled owing to stereoselective H-bonding interactions. Such behavior was used to optimize the chromatographic conditions for separation ofN-(dansyl)-amino acids on HSA.
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    Determination of two metabolites of albendazole, albendazole-sulfoxide and albendazole-sulfone in cow's milk using an HPLC method —A systematic approach to optimise extraction conditions (1998)
    Springer
    Chromatographia 48 (1998), S. 777-784 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Solid phase extraction ; Sample treatment optimisation ; Taguchi method ; Albendazole metabolites ; Milk samples
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Reversed phase HPLC methods for the determination of two metabolites of albendazole in cow's milk are described. Albendazole is an anthelmintic agent used both in veterinary and human practice. Its main metabolites are albendazole-sulfoxide and albendazole-sulfone. The separation of the two metabolites was performed on a μ-Bondapak C-18 column using an acetonitrile/methanol/phosphate buffer as mobile phase, with detection at 290 nm. For the sample preparation of the milk samples we used solid phase extraction. A new sample treatment optimisation procedure is also presented for the sample preparation method. Since sample preparation is a critical step in the analysis of residues in biological samples, the second part of our publication describes an optimisation using Taguchi's methodology that increased recovery, accuracy and reliability. After optimisation of the sample preparation, the limit of detection was 10 ng mL−1 milk and the recovery was 70–80% in the concentration range of 30–1000 ng mL−1 milk for both metabolities.
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    Development and validation of stability indicating high-performance liquid chromatographic assays for ketotifen in aqueous and silicon oil formulations (1998)
    Springer
    Chromatographia 48 (1998), S. 797-802 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ketotifen analysis ; Stability indicating analysis ; Aqueous and oil-based formulations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple and specific high-performance liquid chromatographic (HPLC) method for the analysis of ketotifen in aqueous solutions and silicon oil suspensions is described. The HPLC system is based on a reversed phase μBondapak C18 (30×0.39 cm) column with a mobile phase of phosphate buffer (0.001 M, pH 7.4):methanol: acetonitrile: trimethylamine (29.8:45:25:0.2, by volume) at a flow-rate of 1 mL min−1. The eluent was monitored by UV absorption at 299 nm. Silicon oil-based samples were extracted with HCl (0.05 M) using imipramine as internal standard. The recovery of ketotifen and imipramine was greater than 80%. The calibration curves for both assays were linear over the ranges examined, yielding correlation coefficients greater than 0.997. The assay was shown to be stability indicating by subjecting solutions of ketotifen in phosphate buffer to heat, oxidative stress and irradiation with ultraviolet light (254 and 369 nm)for up to 8 h. The methodology was also shown to be applicable for the analysis of ketotifen in simple aqueous based formulations, in suspension in silicon oil and for the analysis of samples derived fromin vitro skin transfer experiments.
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    An improved method for assay of vitamin C in fish feed and tissues (1998)
    Springer
    Chromatographia 48 (1998), S. 43-47 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Vitamin C analysis ; Ascorbate-2-phosphate and sulphate esters ; Enzyme shifting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method was devised to assay four forms of vitamin C: L-ascorbic acid (AA), dehydroascorbic acid (DHA), ascorbate-2-mono- and polyphosphate (AMP, APP), as well as ascorbate-2-monosulphate (AMS), in sample series of different fish tissues and feed. Direct and indirect detection were combined. Sample extractions were carried out with 0.2 mol L−1 sodium acetate buffer (pH 4.8) and extracts were deproteinized after different chemical or enzymatic reactions, with perchloric acid. The DHA was reduced to AA with dithioerythritol (DTE). Ascorbate oxidase enzyme was used for the detection of background and an acidic phosphatase enzyme for the hydrolysis of different phosphate esters. Ascorbate-2-sulphate was detected directly with help of coinjection of the compound. Chromatographic analysis was carried out with a single column isocratic reverse phase method. The mobile phase was an aqueous buffer of 0.04 M sodium-acetate, 0.05 mM EDTA, 0.5 mM tetrabutylammonium dihydrogen phosphate (TBA) adjusted to pH 3.76 with 85% H3PO4 and with 24 mL methanol added to 1000 mL. C-18 columns were used with 0.6 mL min−1 flow rate at 23°C. The vitamin C forms were detected by UV absorption at 250 nm. The determination limit was 1.0–5.0 μg g−1 in AA equivalent. The standard deviations were between 1–6% and depended on the concentrations of vitamin C forms and tissues. Recoveries were between 90–96% in samples.
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    Liquid chromatography of polymer mixtures by a combination of exclusion and full adsorption mechanisms. Three- and four-component polymer blends (1998)
    Springer
    Chromatographia 48 (1998), S. 65-70 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Multicomponent mixtures ; Separation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Coupling of full adsorption-desorption and size-exclusion chromatography (FAD-SEC) has been applied to the separation and molecular characterization of three- and four-component polymer blends. The method is based on the full adsorption of alln orn−1 components of the polymer blend in a specially designed FAD minicolumn. By appropriate eluent switching the adsorbed polymers are desorbed stepwise from the FAD minicolumn into an on-line SEC column for molecular characterization. It is shown that the desorption isotherms of particular blend components give valuable information about the appropriate displacer composition. The exact position of the desorption isotherms depends, however, both on the amount of polymer adsorbed and in the presence of other, chemically different, polymers within FAD column. The nature and composition of the displacer must, therfore, be adjusted if the intervals between the desorption of particular blend components are to be large enough to prevent displacement overlap.
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    The RP-HPLC analysis of anthocyanins (1998)
    Springer
    Chromatographia 48 (1998), S. 360-364 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Acylated anthocyanins ; Rudbeckia hirta L. ; In vitro cultures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Conditions were determined for the separation of a complex set of anthocyanins (free aglycones, mono- and multiglycosides and esterified forms) by HPLC. The optimised gradient elution method was then used to carry out qualitative and quantitative analysis of anthocyanin compounds present in the callus tissue ofRudbeckia hirta L. and the tubular flowers of the soil-based plant. The summary content of anthocyanin pigments and the content of the main pigment was identified in the analysed biomass. The method developed is useful for the purposes of monitoring the process of biosynthesis of anthocyanins in tissues obtained through in vitro cultures. The advantages of the method for anthocyanins and its application to other anthocyanin-rich materials are also discussed.
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    Effects of amine additives on the resolution of antipsychotic and antidepressant drugs on a cyanoalkyl HPLC column (1998)
    Springer
    Chromatographia 48 (1998), S. 770-776 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Basic drug compounds ; Amino additives ; Cyanoalkyl columns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of basic antidepressant and antipsychotic drugs on a cyanoalkyl-bonded silica column has been studied to determine the effects on peak retention, symmetry, efficiency, and resolution of six different amine mobile-phase additives. The amines—ammonia,n-butylamine, triethylamine,N,N-diisopropylethylamine,N,N-dimethylbutylamine andN,N-dimethyloctylamine—were, except forN,N-diisopropylethylamine, chosen because of their widespread use for improvement of peak symmetry in chromatographic methods;N,N-diisopropylethylamine was included as an example of a sterically hindered amine to see if the stereochemistry around the nitrogen atom is an important consideration in the selection of an additive. This study shows that a gain in symmetry and efficiency is accompanied by loss of resolution. The results obtained also indicate that one type of amine additive should be used when symmetry and efficiency are most important and another when resolution is paramount.
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    Extraction and liquid-chromatographic determination of amphotericin B in oil-water lecithin-based microemulsions (1998)
    Springer
    Chromatographia 48 (1998), S. 803-806 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Amphotericin B ; Oil-water lecithin-based microemulsions ; Extraction of drug from microemulsion ; Reversed-phase HPLC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method employing extraction then reproducible reversed-phase high-performance liquid chromatography (RPHPLC) with monitoring of the drug by absorbance at 405 nm has been developed and validated for the determination of amphotericin B in oil-water lecithin-based microemulsions. The precision and accuracy of the method are excellent (SD 2.4% and 4.2%, respectively). The established linearity range was 10–60 μg mL−1 (r 2=0.9967). The recovery of amphotericin B from spiked placebo was 〉90% over the linear range. The extraction procedure was simple and the HPLC conditions were able to separate the drug from its degradation products and excipients. The method has been used successfully for determining the amphotericin B content of microemulsions and for evaluating the chemical stability of amphotericin B-loaded microemulsions.
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    Studies on shape selectivity of RP C18-columns (1998)
    Springer
    Chromatographia 48 (1998), S. 183-189 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polymeric phases ; Shape selectivity ; PAH selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Stationary phases with octadecyl groups have been prepared with different carbon content without and in the presence of water and characterized for their selectivity for the shape of various polyaromatic hydrocarbons. It is shown that both a high hydrocarbon content and a good accessibility of the bonded groups within the pores is required to achieve shape recognition for PAH. High carbon content alone is not sufficient. The two tests for shape selectivity proposed by Sander and Wise as well as by Tanaka are compared. In most cases the results are similar: A low selectivity with the Sander and Wise test (α TBN/BaP〈1) corresponds to a high value with the Tanaka test (α TRI/o-TER〉3). However, not in all cases the tests give corresponding answers. Further studies on molecular recognition are required.
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    Chiral recognition by molecularly imprinted polymers in aqueous media (1998)
    Springer
    Chromatographia 48 (1998), S. 197-202 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Molecular imprinting ; Molecular recognition ; Chiral recognition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Molecularly imprinted polymers were prepared using 2-vinylpyridine and/or methacrylic acid as functional monomers in a self-assembly imprinting protocol. The resulting polymers were analyzed in aqueous media, and the effects from the pH of the mobile phase and the degree of added organic solvent were investigated. The results are indicative of the importance of ionic bonds in conjunction with hydrophobic interactions in the formation of the complexes between the analyte and the polymers.
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    Dye-coated stationary-phases: A retention model for anions in ion-interaction chromatography (1998)
    Springer
    Chromatographia 48 (1998), S. 190-196 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-interaction chromatography ; Dye-coated reversed phase ; Retention model ; Experimental design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of inorganic anions (NO3 −, NO2 −, Cl−, Br−, I−, SO4 2−, S2O3 2−) by ion-interaction chromatography mediated with a specific dye has been investigated. Chromatography was performed on a LiChrospher RP-18 colum dynamically coated with crystal violet, using acetonitrile-water buffered with phthalate as the mobile phase. The presence of the dye in the eluent enabled indirect spectrophotometric detection of the analytes, which have no significant UV absorption. Retention data were collected for the different anions by varying the composition of the mobile phase according to a full factorial experimental design. A theoretical model for the retention of singly- and doubly-charged analytes, on the basis of the two main processes of ion-exchange and ion-pair formation, has been proposed and validated with the experimental data.
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    Wheat β-amylase behaviour regarding salt promoted adsorption processes (1998)
    Springer
    Chromatographia 48 (1998), S. 209-214 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Covalent chromatography ; Thiophilic and hydrophobic ligands ; Wheat β-amylase ; Salt promoted adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The behaviour of wheat β-amylase from crude extracts in chromatography on agarose gels substituted with different ligand types was investigated. The enzyme displayed high salt promoted adsorption onto thiophilic gels provided with sulfone-thioether and 2-thiopyridine ligands. Quantitative recovery of the enzyme was easily accomplished by elution with buffer in the absence of Na2SO4. The 3-(2-pyridylthio)-2-hydroxypropylagarose (PyS-gel) also allowed elimination of pigments present in the wheat extract. These pigments showed no adsorption onto the gel, thus regeneration is easily achieved, allowing its re-use. The enzyme also displayed strong salt-dependent adsorption onto adsorbents provided with pyridyldisulfide moieties, but in this case enzyme binding was due to its thiol content since elution was achieved mainly through reduction with DTT. When the enzyme was chromatographed on a series of hydrophobic alkyl ligands in the presence of 0.5 M sodium sulphate, it was partially adsorbed on pentylagarose and quantitatively adsorbed on hexyl-agarose, elution being easily performed by sodium sulphate-free buffer. This behaviour was markedly different from that towards phenyl-Sepharose, to which the enzyme was strongly adsorbed and which required much more drastic elution conditions.
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    Retention and column efficiency in reversed phase liquid chromatography as a function of pH for optimization purposes (1998)
    Springer
    Chromatographia 48 (1998), S. 237-244 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chromatographic behavior ; pH optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The effects of pH on both the solute retention and the peak shape of ionogenic compounds are studied in order to propose accurate models for pH optimization purposes. Several mathematical models (theoretical and empirical) for describing the variation of the retention factor versus pH are compared within different pH ranges. Limits of such models used for optimizing the pH by requiring only 3 preliminary experimental runs, are discussed in terms of deviations (≤±5%) of predicted retention times from experimental retention times. An original procedure is developed for selecting the most convenient retention model, from a given set of three retention data. This set is also applied to modeling the variation of both peak width and peak asymmetry with mobile phase pH conditions. Such a procedure is demonstrated as helpful for the separation of ionogenic solutes by considering mobile phase pH as an additional variable that can be useful during optimization procedures.
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    The driving force for solute retention in electron donor-acceptor chromatography: Electrostatic versus charge-transfer interactions (1998)
    Springer
    Chromatographia 48 (1998), S. 523-528 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Retention mechanism ; Donor-acceptor complex ; Molecular interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Charge-transfer interactions are often assumed to be dominant among the noncovalent interactions that govern the solute retention in electron donor-acceptor chromatography. This popular view, however, has been called into question by recent studies that suggest an important role for electrostatic interactions in the formation of donor-acceptor complexes. We reported here an experimental investigation concerning the question as to whether charge-transfer or electrostatic interactions are the driving force for solute retention in donor-acceptor chromatography. Using three chromatographic systems composed of a dinitrobenzene derived stationary phase and a hexane based mobile phase, we determined retention factors for a range of aliphatic and aromatic hydrocarbons and correlated them with molecular properties that describe the solute's dispersion, charge-transfer, and electrostatic characteristics. It was found that the molecular polarizability and ionization potential give either very poor or no correlation with solute retention whereas the molecular quadrupole moment is a linear function of the logarithmic retention factor. These results were interpreted as showing that electrostatic, rather than charge-transfer or dispersion, interactions play a major role in determining solute retention. The dominance of the electrostatic interactions over the other noncovalent interactions was discussed in terms of distance dependency of the interaction energy.
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    Characterization of peak purity by fast multiscan circular dichroism detection (1998)
    Springer
    Chromatographia 48 (1998), S. 584-588 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Circular dichroism detection ; Multiscan detection ; Peak purity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method has been developed to detect inhomogeneity of apparently homogeneous peaks of very similar analytes. The method utilizes the rapid scan feature of state-of-the-art spectrometers/detectors that allow the recording of up to 30 spectra in a single chromatographic peak. Sensitivity and selectivity are enhanced by chiroptical/optical detection. Thus, identification of “front” and “rear” components of the peak can be carried out. The method is exemplified by mixtures of codeine, hydrocodone and oxycodone as analytes.
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    HPLC determination of berberine in plasma of patients with ischemic heart failure (1998)
    Springer
    Chromatographia 48 (1998), S. 589-590 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Berberine in plasma ; Ischemic heart failure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Berberine absorption by patients with ischemic heart failure (IHF) after oral administration and the relationship between clinical effect and plasma berberine concentration are studied. Plasma samples were pretreated by chloroform extraction. Berberine was determined on a μBondapak column with acetonitrile-phosphoric acid mobile phase and UV detection. The limit for berberine in plasma was 8 ng mL−1 for an injection volume of 50 μL. Average berberine recovery was 96.5%. Results showed that improvements in symptoms were more significant for patients with plasma berberine concentration〉0.1 mg L−1 than for those with〈0.1 mg L−1. Plasma berberine monitoring may be helpful in the treatment of patients with IHF.
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    Hexadecyltrimethylammonium bromide/ethanol/water systems as mobie phase in reverse phase high performance liquid chromatography. Study of metal-diethyldithiocarbamate complexes retention (1998)
    Springer
    Chromatographia 48 (1998), S. 517-522 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Micellar liquid chromatography ; Diethyldithiocarbamates ; Metal complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This paper presents the, chromatographic retention of Co(II), Ni(II) and Cu(II) as diethyldithiocarbamate complexes in the presence of hexadecyltrimethylammonium bromide/ethanol/water systems, as mobile phase, by reversed phase high performance liquid chromatography. The presence of an organic modifier reduces the retention times and improves the efficiency. In order to evaluate the interaction between the metal complexes and the mixed micellar system the values of solute binding constants are calculated in, two ways: a) Arunyanart and Cline-Love's treatment and b) multiple regression analysis taking account of the ethanol percentages.
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    An improved high-performance liquid chromatography method for the determination of homocysteine in human plasma (1998)
    Springer
    Chromatographia 48 (1998), S. 506-510 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Homocysteine ; Human plasma ; Routine analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Elevated plasma homocysteine is, a known risk factor in arteriosclerotic vascular disease. To measure homocysteine in a large number of samples, we have developed a rapid, simple, robust and inexpensive reversed-phase HPLC method for routine analysis. Mercaptopro-pionylglycine was used as the internal standard and an external calibration in plasma was performed. Improvement was achieved by the use of gradient elution (using a sodium acetate buffer and methanol) resulting in a higher number of samples analyzed per day. Plasma samples were reduced with tributylphosphine and the proteins were precipitated with perchloric acid before addition of internal standard. The analytes were derivatized by use of 7-fluorobenzofurazone-4-sulfonic acid ammonium salt. For calibration human plasma was spiked with nine different concentrations of homocysteine (range 2–50 μmol L−1). The inter-assay precision of replicate (n=29) analysis of the concentration of homocysteine in a sample of pooled plasma was 3.0%. The limit of detection, defined as three times the signal-to-noise ratio, was 0.25 μmol L−1. The linearity of the assay was confirmed for a plasma concentration range of 2–2000 μmol L−1. The variation of duplicate analyses of 842 plasma samples was 2.6±1.7%.
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    High-performance liquid chromatographic assay for simultaneous determination of tramadol and its active metabolite in human plasma. Application to pharmacokinetic studies (1998)
    Springer
    Chromatographia 48 (1998), S. 555-560 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Tramadol andO-demethyl tramadol in plasma ; Pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A sensitive liquid chromatographic assay for the quantitative determination of the opioid analgesic tramadol and its active metabolite is described. Fluconazole was used as internal standard. The assay involved a singletert-butyl methyl ether extraction and LC analysis with fluorescence detection. Chromatography was at 30°C pumping an isocratic mobile phase of acetonitrile-water (19∶81, v/v) containing 0.06M NaH2PO4 and 0.05M triethylamine, adjusted to pH 7.90, at 1 mL min−1 through a reversed-phase, 250×4 mm base-stable column. The limit of quantitation of tramadol and its active metabolite was 1 ng mL−1, only 0.5 mL plasma sample was required for the determination. The calibration curve was linear from 1–1000 ng mL−1. Intra and inter-day precision (C.V.) did not exceed 10%. Mean recoveries of 96.38% for tramadol and 96.62% forO-demethyltramadol with CVs of 0.43% and 1.46% were obtained. Applicability of the method was demonstrated by a pharmacokinetic study on normal volunteers who received 100 mg tramadol intravenously.
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    A methodological and metabolite identification study of the metabolism of S-carboxymethyl-L-cysteine in man (1998)
    Springer
    Chromatographia 48 (1998), S. 561-568 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Planar chromatography ; S-Carboxymethyl-L-cysteine ; Metabolic studies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The analysis of 08:00–16:00 (0–8) hour urine collections following oral S-carboxymethyl-L-cysteine administration of 750 mg to 30 individuals identified S-carboxymethyl-L-cysteine, S-carboxymethyl-L-cysteine S-oxide, S-methyl-L-cysteine and S-methyl-L-cysteine S-oxide as the major urinary drug related compounds. No S-(carboxymethylthio)-L-cysteine mixed disulphide metabolite was found in the 08:00–16:00 hour urine collection but the metabolite was detected in the 16:00–00:00 (8–16) hour urune collection by paper chromatography, TLC and HPLC. The production of the S-oxide metabolites 08:00–16:00 hour urine collection) and the mixed disulphide metabolite (16:00–00:00 hour urine collection) were both shown to be biomodally distributed. A significant linear correlation of the S-oxides recovered following 08:00–16:00 hour urine collection as analysed by paper chromatography, TLC and HPLC is reported.
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    URL: http://dx.doi.org/10.1007/BF02466650
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    Normal phase gradient polymer elution chromatography of polyester resins (1998)
    Springer
    Chromatographia 48 (1998), S. 623-630 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Normal phase gradient elution ; Polyester resins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Polymers can be characterized by gradient elution techniques in order to obtain information on their chemical composition and molar mass. In this paper, features and applications of Normal Phase Gradient Polymer Elution Chromatography (NP-GPEC) for the characterization of (co)polyesters are investigated. Two polyesters were characterized, using various stationary and mobile phases. Separation was shown to be dominated by end groups in most cases, and to a lesser extent by molar mass. A distinct influence of both column type and mobile phase type was observed. A polymer based polyamine (PA) column povided the best results, although no complete separation between the mono- and di-acid fractions could be obtained. In all cases, separation was governed by sorption rather than by precipitation/redissolution. NP-GPEC was shown to be a potentially interesting technique for the characterization of copolyesters according to the chemical composition of the backbone, independent of end groups.
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    High performance liquid chromatographic analysis of theIn vitro N-dealkylated andN-oxide metabolites ofN-ethyl-N-methylaniline: Methodology for the determination of enzyme activity and stereoselectivity ofN-oxidation (1998)
    Springer
    Chromatographia 48 (1998), S. 664-670 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Enantiospecific analysis ; N-Ethyl-N-methylaniline ; N-Oxidation ; N-Dealkylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A robust, sensitive reverse-phase high-performance liquid chromatographic (HPLC) method for the quantification of the majorin vitro oxidative microsomal metabolites of the prochiral tertiary amineN-ethyl-N-methyllaniline (EMA) is described. The analytes were resolved on a Spherisorb 5 ODS1 HPLC column using an acetonitrile/phosphate buffer system under isocratic conditions. Use of solid-phase extraction (SPE) and ultraviolet (UV) detection at low wavelength (210 nm) enabled the detection of EMAN-oxide simultaneously with the majorN-dealkylated metabolites,N-ethyl andN-methylaniline. Previous chromatographic methods described for the quantification ofN,N-dialkylarylamineN-oxides have generally required sample pretreatment to reduce theN-oxide to its parent tertiary amine prior to analysis. The above method, in combination with a previously reported chromatographic resolution based on the Chiralcel OD chiral stationary phase (CSP), allows accurate and precise determination of both the quantity and stereochemical composition of metabolically derived EMAN-oxide.
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    High performance liquid chromatographic separation of chlorophyllc forms from marine phytoplankton on octylsilica bonded phases (1998)
    Springer
    Chromatographia 48 (1998), S. 677-680 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chlorophyllc ; Marine phytoplankton ; Octylsilica phases ; Photosynthetic pigments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of mono- and divinyl chlorophyllc forms was estudied employing several octylsilica and octadecylsilica columns under isocratic conditions. In this paper we show that, using the adequate mobile phases, the monomeric C8 columns can separate the mentioned chlorophylls. A comparison between C8 and C18 columns reveals that monomeric OS phases provide always higher resolution of the MV- and DV chlorophyllc pairs. Such a result could be explained in terms of differences in column polarity. When adequate gradient profiles and injection conditions are used the separation is accomplished together with that of other chlorophylls and carotenoids.
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    Ligand-exchange chromatographic separation of DL-amino acids on aminopropylsilica-bonded chirals-triazines (1998)
    Springer
    Chromatographia 47 (1998), S. 637-642 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ligand-exchange chromatography ; Chiral stationary phases ; Enantiomer separation ; Amino acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Chiral stationary phases (CSPs) were synthesized by reaction of aminopropylsilica (APS) with chiral monochloro-s-triazines (MCTs). MCTs were obtained by reaction of 2,4,6-trichloro-s-triazine (cyanuric chloride) with one equivalent of methanol and, subsequently, with one equivalent of L-prolinetert butyl ester (H-Pro-OtBu) orN-tert butyloxycarbonyl-L-lysinetert butyl ester (Boc-Lys-OtBu). End-capping of unreacted amino groups of APS with acetic anhydride, followed by trifluoroacetolytic cleavage of the protecting groups of amino acids (AAs), afforded two chiral stationary phases bearing either L-proline (CSP-3) or L-lysine (CSP-4) as chiral selector. Using ligand-exchange chromatography matography with addition of Cu2+ to the mobile phase, enantiomers of free DL-AAs and a fewN-(2,4-dinitrophenyl)-DL-AAs were separated on CSP-3, whereasN-(dansyl)-DL-AAs were separated on CSP-4.
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    Determination of glucuronides of molecules of toxicological interest by liquid chromatography negative-ion mass spectrometry with atmospheric pressure chemical ionization (1998)
    Springer
    Chromatographia 47 (1998), S. 659-666 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Atmopheric Pressure Chemical Ionization (APCI) mass ; spectrometry ; Glucuronide-conjugates ; Toxicological compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new chromatographic method for the direct determination of metabolites (glucuronide-conjugates) of molecules of toxicological relevance in biological media with the minimum sample pre-treatment has been developed. A high performance liquid chromatographyatmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) system was used for this purpose. The separation of four glucuronides Aminophenylglucuronide (APhG), Phenylglucuronide (PhG),p-Nitrophenylglucuronide (NPhG) and α-Naphthylglucuronide (NG) was obtained under ion-suppressed reversed-phase chromatography conditions, by using high-speed (3 cm, 3 μm) columns and formic acid (2 mM) as the acid modifier in the mobile phase. Different C-18 stationary phases (partially endcapped and non-endcapped) were evaluated in order to obtain retention for these very polar, water soluble molecules. The ionization of the analytes was obtained in negativeion (NI) mode. Detection limits were in the range 1–5 mg L−1 and calibration curves were linear over two order of magnitude. Intra-day and inter-day precision were in the range 2.9–10.6% for all the compounds. The method was successfully applied for the determination of PhG in a urine sample of a European Quality Assurance Programme for Organic Solvent Metabolites.
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    Direct solid-phase microextraction combined with gas and liquid chromatography for the determination of lidocaine in human urine (1998)
    Springer
    Chromatographia 47 (1998), S. 678-684 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Column liquid chromatography ; Solid-phase microextraction ; Local anaesthetic lidocaine ; Optimisation of extraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Solid-phase microextraction (SPME) has been combined with gas chromatography (GC) and liquid chromatography (LC) for the determination of lidocaine in human urine. A polydimethylsiloxane (PDMS) coated fibre was directly immersed into buffered urine. Extraction conditions such as time, pH, ionic strength, temperature, and agitation were optimised. The extracted lidocaine was thermally desorbed in a split/splitless injector for analysis with a GC-FID system or desorbed with liquid in a specially designed SPME-LC interface for analysis with an LC-UV system. After optimisation the method developed was evaluated and validated. Extraction yields of 22% were obtained in about 45 min. The reproducibility of the method is 〈5% (relative standard deviation). For five-times diluted urine, linear ranges were found from 5–1000 and 25–1000 ng·mL−1 for SPME-GC and SPME-LC, with detection limits of 5 ng·mL−1 for SPME-GC and 25 ng·mL−1 for SPME-LC. SPME can be used as a simple sample pretreatment method for the determination of lidocaine in urine by GC and LC.
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    Experimental and statistical approach for validating and HPLC assay for the determination of vitamin a in flour and milk powder for children (1998)
    Springer
    Chromatographia 47 (1998), S. 716-720 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Vitamin A in flour and milk powder ; Method validation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An experimental and statistical approach is presented which enables, with a minimum of determinations, the validation of a high-performance liquid chromatographic (HPLC) method for the determination of vitamin A in milk powder and flour for children. The principal aspects of method validation are examined and discussed.
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    URL: http://dx.doi.org/10.1007/BF02467459
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    Group separation of organic nitrates on a new nitric acid ester NP-LC stationary phase (1998)
    Springer
    Chromatographia 47 (1998), S. 157-163 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Nitric acid ester phase ; Alkyl nitrates ; Group separation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The synthesis of a nitric acid ester NP-LC stationary phase (organonitrate phase), by nitrating a commercial polyol phase (Serva, Polyol Si 100, 5 μm) with mixed sulfuric-and nitric acid, is reported. The nitric acid ester bond is quite stable towards hydrolysis. To examine its possible use as a stationary phase for the group separation of alkyl nitrates, several bifunctional polar alkyl nitrates (di-nitrates, hydroxy-nitrates, keto-nitrates) have been synthesized. In order to simplify their names a new abbreviating nomenclature for multifunctional organic nitrates is presented. With our new stationary phase it is possible to separate mono-, di-, and hydroxy-nitrates as groups completely, a major advantage in sample preparation in the chemistry of smog formation. However a co-elution of di- and keto-nitrates is observed. A distinction of the latter two organonitrate groups is possible by gas chromatography-mass spectrometric detection (MSD). Apart from the fragment ion NO2 + (m/z=46 amu), which is nearly specific for alkyl nitrates, aliphatic di- and keto-nitrates show different characteristic fragment ions.
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    Liquid chromatographic analysis of non-volatile strawberry compounds (1998)
    Springer
    Chromatographia 47 (1998), S. 197-202 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Non-volatile strawberry compounds ; Multivariate analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A procedure is presented for simultaneous extraction of organic acids, vitamin C and sugars from strawberries and analysis by reversed-phase (RP) HPLC and cationexchange (calcium form) chromatography. Recoveries from strawberries spiked at different levels ranged from 96 to 103 % for carbohydrates, 92 to 112 % for organic acids, and 84 % for vitamin C; the repeatability of the method evaluated as the relative standard deviation in the optimum range was 〈5 % for sugars and 7.5 % for organic acids and vitamin C. Multivariate analysis techniques, such as Bayes and SIMCA analyses, have enabled correct classification of the strawberries tested but we were unable to establish adequate models for typifying them according to their geographic origin.
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    URL: http://dx.doi.org/10.1007/BF02466581
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    The application of high performance liquid chromatography, coupled to nuclear magnetic resonance spectroscopy and mass spectrometry (HPLC-NMR-MS), to the characterisation of ibuprofen metabolites from human urine (1998)
    Springer
    Chromatographia 47 (1998), S. 264-270 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; NMR and MS detection ; Ibuprofen metabolites ; Urine extracts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The use of HPLC-NMR-MS for the detection and identification of the metabolites of ibuprofen present in a solid phase extract of human urine is described. Gradient reversed-phase HPLC was used to separate the components present in the extract, which were then characterised by a combination of stopped-flow1H NMR and on line electrospray-MS. This approach led to the rapid identification of the known phase 1 human metabolites of ibuprofen, including hydroxy- and carboxy- metabolites, together with their respective glucuronide conjugates. In addition a probable artefact resulting from the dehydration of one of the side chainhydroxylated glucuronides was also identified.
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    Use of short columns and high flow rates for rapid gradient reversed-phase chromatography (1998)
    Springer
    Chromatographia 47 (1998), S. 291-298 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Capillary electrochromatography ; Rapid analysis ; Short columns ; Rapid gradients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Rapid analyses were performed using reversed-phase liquid chromatography with short (20–100 mm) columns swept by fast yet shallow gradients, and the results compared with those obtained with 150 mm columns and slow gradients. The resolution losses incurred with shorter columns were minimised by employing elevated flow rates, to ensure that comparable mean retention factors were experienced by individual analytes during gradients run on different columns. This conserves gradient steepness. High quality performance was obtained with turn-around times of 5–10 minutes. An overall 5-fold enhancement in the rate of information generation was obtained. The relevance of instrumental parameters and of column and packing dimensions, upon the potential for improved performance is discussed. Some implications for the rapidly developing technique of capillary electrochromatography are briefly indicated.
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    Correlation between the chromatographic poperties of silica phenyl packing materials and the retention behaviour of methylated β-cyclodextrins (1998)
    Springer
    Chromatographia 47 (1998), S. 383-390 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Stationary phase characterization ; Silica packing materials ; Cyclodextrins ; Partially methylated β-cyclodextrins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The chromatographic properties of five columns packed with phenyl-bonded phases were characterized by an approach based on Tanaka's method for column to column comparisons in order to develop an LC analysis of partially methylated β-cyclodextrins. The retention behaviour of β-cyclodextrin, heptakis(2,6-di-O-methyl)-β-cyclodextrin and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin was examined in order to evaluate the different interactions between phenyl stationary phase and this family of compound. Chromatograms show that the residual silanol activity of the packing materials plays a beneficial role in the partially methylated β-cyclodextrins separation process. It is concluded that knowledge of the interactions involved allows one to make a reasoned choice of the stationary phase in order to obtain the best possible analysis of three different commercial samples of partially methylated β-cyclodextrins.
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    Rapid determination of ranitidine in human plasma by high-performance liquid chromatography (1998)
    Springer
    Chromatographia 47 (1998), S. 391-395 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ranitidine ; Plasma ; Pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An HPLC method has been developed for the quantification of rantidine in plasma for pharmacokinetic studies. Metoclopramide was used as internal standard. The method uses a simple and rapid sample clean-up procedure involving single-step extraction with organic solvent to extract ranitidine from plasma. After evaporation and reconstitution the samples are chromatographed on a 250 mm×4 mm base-stable reversed-phase column with 0.05 M ammonium acetate-acetonitrile, 75∶25 (v/v) as mobile phase and UV detection at 313 nm. The calibration graph was linear for quantities of ranitidine between 10 and 2000 ng mL−1. Intra- and inter-dayCV did not exceed 11.64%. The quantitation limit was 10 ng mL−1 for human plasma. The applicability of this method for pharmacokinetic studies of ranitidine after oral administration are described. Approximately 90 samples can be processed in 24 h.
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    A new validated high-performance liquid chromatographic method for the determination of EGIS-9933 in rat plasma (1998)
    Springer
    Chromatographia 48 (1998), S. 158-162 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; EGIS-9933 ; Solid phase extraction ; Rat plasma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new highly sensitive high-performance liquid chromatographic (HPLC) procedure for determination of EGIS-9933 (a newly developed anxiolytic compound) in rat plasma is described. A gradient, elution method with UV detection at 270 nm has been developed using a mobile phase of a mixture of A: methanol:acetonitrile 1:9 and B:0.5% triethilamine in water, the pH of B was adjusted to 3 with phosphoric acid. Solid phase extraction (SPE) was used for the sample preparation. The calibration was linear in the 10–10000 ng mL−1 concentration range. The limit of quantification was 10 ng mL−1. The bioanalytical method was validated according to internationally accepted criteria for biological samples.
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    Ion-pair HPLC determination of biogenic amines and precursor aminoacids. Application of a method based on simultaneous use of heptanesulphonate and octylamine to some foods (1998)
    Springer
    Chromatographia 48 (1998), S. 763-769 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-pair chromatography ; Food related-biogenic amines ; Heptanesulphonate ; Octylamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An ion-pair HPLC method based on the simultaneous use of heptanesulphonate and octylamine has been considered with the aim of optimizing the separation of four food-related biogenic amines (histamine, tyramine, 2-phenylethylamine and tryptamine) and related precursor aminoacids. On changing the eluant pH from 2.70 to 3.20 the capacity factor of precursor aminoacids decreased and those of the biogenic amines increased; pH 3 allowed an optimal separation. An increase of phosphate content, from 6.0 mM to 12.0 mM, shortened the capacity factors. The addition of octylamine to the eluant reduced the peak asymmetry (especially for histamine from 3.20 to 1.69). Some samples of cheese showed a concentration of total amines up to 1284.8 mg L−1; wines and beers showed a very similar total content, ranging from 0.5 mg L−1 to 27.2 mg L−1.
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    Supercritical fluid extraction of bile acids from bovine bile raw materials (1998)
    Springer
    Chromatographia 48 (1998), S. 785-789 
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    ISSN: 1612-1112
    Keywords: Gas chromatography-mass spectrometry ; Column liquid chromatography ; Supercritical fluid extraction ; Bile acids ; Bovine bile hydrolysates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The use of supercritical fluid extraction (SFE) as an alternative to conventional liquid extraction has been investigated to conventional liquid extraction has been investigated for the isolation of bile acids (cholic acid, deoxycholic acid and chenodeoxycholic acid) from the solid material obtained by bovine bile hydrolysis. Initial studies indicated that bile acids are not soluble in supercritical CO2, consequently the addition of the polar modifier methanol to the CO2 extracting fluid was evaluated. Quantitative recoveries (〉88.5%) were obtained for the bile acids in 20 min with 15% (v/v) methanol in CO2 at 220 atm and 70°C. A comparison of SFE with pyridine extraction was performed on samples of hydrolyzed crude bovine bile. The SFE method yielded recoveries higher than 82.7% compared with conventional liquid extraction. Moreover, SFE minimized sample handling, reduced the consumption of harmful solvents and provided conditions suitable for selective extractions of bile acids from bovine bile raw materials.
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    Enantiomeric resolution of melatonin ligands receptors by liquid chromatography on amylose chiral stationary phases (1998)
    Springer
    Chromatographia 48 (1998), S. 790-796 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chiral-enantiomeric separation ; Amylose-based chiral phases ; Melatonin analogues ; Tetrahydronaphthalenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Analytical HPLC methods using derivatized amylose chiral stationary phases were developed for the resolution of enantiomers of methoxy an ethyl tetrahydronaphthalenic derivatives, new agonist and antagonist ligands for melatonin receptors. Separation was by normal phase methodology with a mobile phase ofn-hexane-alcohol (methanol, ethanol, 1-propanol or 2-propanol) in various proportions, and a silica-based, amylose tris-(S)-1-phenylethylcarbamate (Chiralpak AS), or tris-3,5-dimethylphenylcarbamate (Chiralpak AD). The mobile phase and the chiral stationary phase were optimized for best resolution. The effects of concentration of alcohol, various aliphatic alcohols in the mobile phase were studied. The effects of substitution were analysed. Baseline separation (Rs〉1.5) was easily obtained in man cases.
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    Analysis of cannabinoids in fiber hemp plant varieties (Cannabis sativa L.) by high-performance liquid chromatography (1998)
    Springer
    Chromatographia 48 (1998), S. 215-222 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Neutral and acidic cannabinoids ; Fiber hemp plants ; Cannabis accessions and environmental conditions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An analytical procedure was developed for the detection of neutral and acidic cannabinoids in herbal cannabis without the need of any preliminary derivatization. The method was used to assay cannabinoid content of over one hundred fiber hemp samples grown in different Italian localities and harvested at different maturation level degrees during the summer. No interferences were observed due to the vegetal matrix. The influence of genetic factors and environmental conditions on cannabinoid content is discussed; the results may be of interest to enhance potential of fiber hemp in compliance with law enforcement purposes.
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    An improved analytical method for determination of heterocyclic amines in chicken legs (1998)
    Springer
    Chromatographia 48 (1998), S. 223-230 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Heterocyclic amines ; Chicken legs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Several extraction, separation and detection methods for heterocyclic amines (HAs) in chicken legs were evaluated by liquid chromatography. Results showed that the most appropriate extraction method includes the removal of macrosubstances by centrifugation and subsequent purification using a PRS (propylsulfonic acid silica gel) and a C18 cartridge, and the recovery obtained ranged between 51 and 89 %. For HPLC separation, a binary solvent system consisting of acetonitrile and 0.05 M ammonium acetate solution (pH 3.6) with gradient elution with flow rate of 1.0 mL min−1 and detection at 258 nm was used to resolve 16 HAs. With fluorescence nine HAs could be detected by employing a programmable wavelength, and the sensitivity was 100–400 times higher than that by UV detection. The detection limits for UV and fluorescence detection were 0.02≈0.5 ng and 0.05≈3 pg respectively, with a signal-to-noise ratio 3. The presence of HAs in fried chicken legs was also determined.
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    Preparation and characterization ofp-tert-butyl-calix[6]arene-bonded silica gel stationary phase for high-performance liquid chromatography (1998)
    Springer
    Chromatographia 48 (1998), S. 245-250 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Calix[6]arene ; Positional isomers ; PAHs ; Nucleosides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary For the first time calix[6]arene has been chemically combined with silica gel via a longer spacer to prepare calix[6]arene-bonded silica gel stationary phase for high-performance liquid chromatography (HPLC). The separation of positional isomers and polycyclic aromatic hydrocarbons on the calix[6]arene-bonded phase was achieved with methanol-water as mobile phase. Some nucleosides were also separated on the bonded phase. The reversed-phase chromatographic performance of the bonded phase was studied. The results showed that the calix[6]arene-bonded phase was highly hydrophobic. A possible separation mechanism has been proposed.
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    URL: http://dx.doi.org/10.1007/BF02467678
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    Evidences for temperature-dependent mechanism of host-guest complexation (1998)
    Springer
    Chromatographia 48 (1998), S. 377-382 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Host-guest complexation ; Temperature effects ; Cyclodextrin inclusion complexes ; Polycyclic aromatics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary High-performance liquid chromatography and ultraviolet spectroscopy methods were applied to the studies on the influence of temperature on the complexation of β-cyclodextrin with naphthalene and its derivatives. The strong nonlinearity of Van't Hoff plots suggests, that the retention mechanism of hydrocarbons investigated might be different in high and low temperature region. The total lack of correlation (r=−0.230) between chromatographic data (capacity factors ratio:k PAH/k PAH×CD) and spectrophotometric data (ΔA) at high temperature (60°) as well as a significant correlation (r=0.922) at subambient temperature (15°C) suggest, that the inclusion mechanism starts to be important at low temperature region and the predominant mechanism for chromatographic retention is the formation of an inclusion complexes in the mobile phase.
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    URL: http://dx.doi.org/10.1007/BF02467707
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    Extraction of polypropylene additives and their analysis by HPLC (1998)
    Springer
    Chromatographia 48 (1998), S. 491-496 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polypropylene additives ; Extraction methods ; Antioxidants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The polypropylene additives were extracted by dissolution-precipitation and Soxhlet. The Soxhlet method was adapted for the extraction of phosphorous antioxidants. The RP HPLC method with quaternary gradient elution separated five chemical groups of additives: lower molecular mass di-tert-butyl phenol (D.T.B.P.), hindered amine light stabilizers (Tinuvin 326), hindered phenolic antioxidants (Irganox 1010) and phosphorous antioxidants (Irgafos 168 and Ultranox 626) with their degradation products.
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    URL: http://dx.doi.org/10.1007/BF02466639
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    Synthesis and characterization of long chain alkyl stationary phases on a silica hydride surface (1998)
    Springer
    Chromatographia 48 (1998), S. 631-636 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Synthesis of new phases ; Evaluation of new phases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary C22 and C30 alkyl chains were attached to a silica hydride surface by a hydrosolation reaction. In each case both moieties were successfully bonded by either metal complex catalysis or free radical initiation. Carbon analysis, DRIFT spectra and13C CP-MAS NMR spectra confirm the bonding of the olefin to silica hydride. Conditions for maximum coverage were determined by a simplex procedure. Chromatographic evaluation of these long chain bonded phases was accomplished by separations of several types of mixtures: alkyl substituted benzenes; polycyclic aromatic hydrocarbons; carotenoids, tocopherols; tricyclic antidepressants; and peptides. The C30 column proved significantly better for separating the carotenoid and antidepressant mixtures and somewhat better for the peptide sample.
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    URL: http://dx.doi.org/10.1007/BF02467592
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    A modified HPLC method for analysis of PSP toxins in algae and shellfish from china (1998)
    Springer
    Chromatographia 48 (1998), S. 671-676 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Paralytic shellfish poisoning (PSP) ; Alexandrium tamarense
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Improvements to an established HPLC method are introduced. The modified method is more efficient for separation and detection of the toxins reponsible for paralytic shellfish poisoning (PSP). The PSP toxin cotent of two strains ofAlexandrium tamarense and approximately forty shellfish samples collected from different locations in China have been analyzed with this HPLC method. Only one shellfish sample, collected from Lianyungang, China, contained PSP toxins.
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    URL: http://dx.doi.org/10.1007/BF02467597
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    Determination of reduced-form glutathione and total glutathione in blood and plasma by high performance liquid chromatography with on-column fluorescence derivatization (1998)
    Springer
    Chromatographia 48 (1998), S. 690-694 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; On-column fluorescence derivatization ; Blood and plasma ; Glutathione ; ortho-Phthalaldehyde
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An on-column fluorometric derivatization method has been developed for the determination of reduced-form glutathione and total glutathione in blood and plasma by high-performance liquid chromatography. Blood hemolysate or diluted plasma was deproteinized with percholoric acid. For total glutathione determination, any oxidized forms of glutathione in samples were converted to reduced-form glutathione with dithiothreitol prior to protein precipitation. Deproteinized samples were injected without pretreatment. Glutathione was fluorescence-derivatized and separated on a C18-bonded vinyl alcohol polymer column withortho-phthalaldehyde in sodium borate buffer-acetonitrile, as mobile phase; theortho-phthalaldehyde-glutathione, fluorescent isoindole adduct is measured by its fluorescence response. Due to the high sensitivity, selectivity reproducibility and the simple HPLC system, the method is particularly suitable for routine assay of numerous or small amounts of samples.
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    URL: http://dx.doi.org/10.1007/BF02467600
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    Survey of concentration of polycyclic aromatic hydrocarbons in lake balaton by HPLC with fluorescence detection (1998)
    Springer
    Chromatographia 48 (1998), S. 149-153 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polycyclic aromatic hydrocarbons ; Lake Balaton ; Water and sediment samples
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Concentrations of polycyclic aromatic hydrocarbons (PAHs) were determined in water and sediment samples at 15 sites in Lake Balaton during three sampling campaigns in 1996. PAHs were concentrated from water samples by solid phase extraction. Sediment samples were extracted with acetone in an ultrasonic bath then cleaned by solid phase extraction. The total concentration of PAHs ranged from 30–360 ng g−1 and from 170–720 ng L−1 in sediment and water samples, respectively. Spatial and temporal variations of the concentration of PAHs were also investigated.
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    URL: http://dx.doi.org/10.1007/BF02467532
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    A simple model for RPLC retention and selectivity of imidazole enantiomers using β-cyclodextrin as chiral selector (1998)
    Springer
    Chromatographia 48 (1998), S. 388-394 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Imidazole derivatives ; β-Cyclodextrin ; Enantioselectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Using reversed phase liquid chromatography (RPLC), this paper investigates the enantioselectivity variations, in a series of weak polar R, S-imidazole derivatives, with β-cyclodextrin concentration in the mobile phase over a wide range of column temperatures. These compounds are used for the treatment of onychomycosis. The selectivity data obtained were assessed using a chiral recognition model, based on the formation of complexes between the solute molecule and the cyclodextrin cavity. Gibbs Helmholtz parameters (Δ(ΔH), Δ(ΔS)) between R- and S- enantiomers were determined from the logarithm of the separation factor, α, versus the reciprocal of the temperature plots. The thermodynamic results predicted that the enantioselectivity mechanism was related to both the solute's bulkiness and the asymmetric carbon atom configuration.
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    URL: http://dx.doi.org/10.1007/BF02467709
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    Ion-exchange chromatography with an oxalic acid-α-hydroxyisobutyric acid eluent for the separation and quantitation of rare-earth elements in monazite and xenotime (1998)
    Springer
    Chromatographia 48 (1998), S. 407-414 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-exchange ; Rare-earth elements ; Monazite ; Xenotime
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An oxalic acid-α-hydroxyisobutyric acid eluent has been used for the separation and determination of rare-earth elements by high-performance ion-exchange chromatography. Fifteen rare-earth elements were separated within less than 25 min on a 150×4.6 mm i.d. column packed with 5-μm sulfonic acid-bonded silica particles by elution with a combined gradient of 0.60–9.0 mM oxalic acid and 19.0–5.0 mM α-hydroxyisobutyric acid at pH 4.6. Detection and quantitation of the separated rare-earth elements was accomplished by visible-absorbance measurements at 600 nm after postcolumn reaction with arsenazo I. The gradient of the two complexing agents was optimized to enable the separation of yttrium(III) without interference from other elements, especially dysprosium(III) and terbium(III). Mass detection limits of the elements were in the range of 2–4 ng. Finally, the chromatographic system was applied to the quantitative analysis of rare-earth elements in monazite and xenotime.
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    URL: http://dx.doi.org/10.1007/BF02467712
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    Potential of short-column liquid chromatography with tandem mass spectrometric detection for the rapid study of pesticide degradation (1998)
    Springer
    Chromatographia 48 (1998), S. 475-480 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Short-Column LC ; Environmental water samples ; MS-MS detection ; Pesticide degradation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The applicability of solid-phase extraction-LC using two short columns (SPE-LC) and/or single-short-column liquid chromatography (SSC) combined on-line with tandem mass spectrometry (MS) was demonstrated for the rapid study of pesticide degradation. A fast analytical procedure was developed to provide preliminary information concerning experimental conditions, approximate rates of degradation and identity of the degradation products. Surface water samples were spiked at relevant concentration levels with well-known microcontaminants and photolysis was used to transform parent compounds into their degradation products. In general, the strategy was as follows: at 30-min intervals 10-mL samples were on-line enriched, separated by short-column LC and recorded in full-scan MS to obtain information on the disappearance of the parent compound and the appearance of breakdown products. To obtain structural information, product-ion spectra of selected compounds appearing in the full-scan MS chromatogram were recorded; this enabled the identification of several degradation products. Total analysis time of enrichment/separation and detection was about 10–15 min.
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    URL: http://dx.doi.org/10.1007/BF02466637
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    Simultaneous determination of base/neutral and acid herbicides in natural water at the part per trillion level (1998)
    Springer
    Chromatographia 48 (1998), S. 497-505 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; MS detection ; Trace herbicides ; Natural waters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new method for the simultaneous identification and quantification of base/neutral and acidic pesticides at a low nanogram per liter concentration level in natural waters is presented. The method includes enrichment of the compounds by solid phase extraction on graphitized carbon black, followed by sequential elution of the base/neutral and acidic pesticides. Identification and quantification of the compounds is performed with HPLC-ESI-MS. This procedure involves passing 1 L of ground water and 2 L of drinking water samples through a 0.5 g graphitized carbon black (GCB) extraction cartridge. A conventional 4.6-mm-i.d. reversed phase LC C-18 operating with a 1 mL min−1 flow of the mobile phase was used to chromatograph the analytes. A flow of 100 μL min−1 of the column effluent was diverted to the ESI source. The ESI source was operated in positive ion mode for base/neutral pesticides and in negative-ion mode for acid pesticides. For the analyte considered, the response of the mass detector was linearly related to the amount of the analytes injected between 5 and 250 ng. In all cases, recoveries of the analytes were better than 90%. The limit of detection (signal-to-noise ratio=3) of the method for the pesticides considered in drinking water samples was estimated to be about 3–10 ng L−1.
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    URL: http://dx.doi.org/10.1007/BF02466640
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    Determination of alkylphenols in water samples by solid-phase extraction on to poly(styrene-divinylbenzene) and quantification by liquid chromatography with UV-detection (1998)
    Springer
    Chromatographia 48 (1998), S. 707-713 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Solid-phase extraction ; Alkylphenols in water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method for determination of alkylphenols in water samples has been developed and validated. The alkylphenols were extracted on to polystyrene solid-phase columns. Six replicates could be processed in parallel in approximately 30 min using home-made equipment. Quantification was performed by reversed-phase liquid chromatography with UV-detection at 278 nm. The method has been validated for determination of 4-n-hexylphenol, 4-tert-octylphenol and nonylphenol in the concentration range 1–100 μg L−1 with 4-n-heptylphenol and/or 4-n-octylphenol as internal standard(s). The repeatability of the method was 1–6%RSD, and the intermediate precision was 1–3%RSD at the 100 μg L−1 level. The accuracy, determined as recovery, was 98–104%. The limit of detection (LOD) was 0.1–0.2 μg L−1 for 1-L water samples. The method has been used for determination of alkylphenols in samples of aquarium water.
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    URL: http://dx.doi.org/10.1007/BF02467603
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    Study of the influence of electronic effects on the retention of substitutedN-benzylideneanilines in normal-phase liquid chromatography (1998)
    Springer
    Chromatographia 47 (1998), S. 164-170 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; N-Benzylideneanilines ; Hierarchical ascending classification ; Correspondence factor analysis ; Electronic effects ; Quantitative structure-retention relationships
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A series of 72 substitutedN-benzylideneanilines (NBA) has been studied by normal-phase liquid chromatography by use of an experimental design based on variation of the composition of mobile phases prepared from heptane and three modifiers, tetrahydrofuran, 1-octanol and ethyl acetate, for each of which the specific interactions are different. Seven mobile phases were defined in the experimental design. The chromatographic data obtained are used to discuss the behavior of NBA by application of complementary chemometric methods—hierarchical ascending classification (HAC) and correspondence factor analysis (CFA). Although solute polarity has the greatest effect on retention, construction of HAC and CFA plots shows that solute behavior is also influenced by second-order electronic effects arising as a result of specific interactions between the solutes and the different modifier solvents. A quantitative structure-retention relationship has been established between Hammett's constants and the solutes projection on the first factorial axis of CFA.
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    URL: http://dx.doi.org/10.1007/BF02466576
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    Interlaboratory study of analysis of phenoxymethylpenicillin by liquid chromatography (1998)
    Springer
    Chromatographia 47 (1998), S. 152-156 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Phenoxymethylpenicillin ; Collaborative study
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A liquid chromatography method for analysis of phenoxymethylpenicillin has been examined in a collaborative study involving 6 laboratories. The method comprised an isocratic part, which is used in the assay. When the isocratic part is combined with gradient elution, the method is suitable for purity control. Five samples of phenoxymethylpenicillin (potassium salts and acid) were analysed. The main component, the most important side product 4-hydroxyphenoxymethyl-penicillin and other impurities were determined. An analysis of variance proved the absence of consistent laboratory bias. Laboratory-sample interaction was not significant. Estimates of the repeatability and reproducibility of the method, expressed as standard deviations (SD) of the result of the determination of phenoxymethylpenicillin, were 0.50 and 0.63 respectively.
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    URL: http://dx.doi.org/10.1007/BF02466574
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    Bile acids as stationary phase in liquid chromatography (1998)
    Springer
    Chromatographia 47 (1998), S. 183-188 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Bile acid aggregates as stationary phase ; Enantiomeric separation ; 1,1′-Binaphthyl-2,2′-diyl-hydrogenphosphate enantiomers ; Dansyl amino acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Bile acids chemically bonded onto aminopropylsilica have been employed as stationary phases in liquid chromatography. Bile acid aggregates were dynamically formed around molecules chemically anchored on the supports when the eluent contained bile salts. The bile salt aggregates achieved the separation of 1,1′-binaphthyl-2,2′-diyl-hydrogenphosphate enantiomers and dansyl amino acids.
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    The chromatographic behavior of arsenic compounds on anion exchange columns with binary organic acids as mobile phases (1998)
    Springer
    Chromatographia 47 (1998), S. 257-263 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion exchange chromatography ; Anion-exchange chromatography ; Arsenic compounds ; Flame atomic absorption detector
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Identification and quantification of arsenic compunds was performed with high- performance liquid chromatography (HPLC) and flame atomic absorption spectrometry (FAAS) as element-specific detector. Arsenous acid, methylarsonic acid, dimethylarsinic acid, arsenic acid, arsenobetaine, and arsenocholine were separated on two anion-exchange columns (Synchropak Q 300 and PRP-X 100) with different binary organic acids as mobile phases. The infleunce of chromatographic parameters, such as pH and the concentration of the mobile phase were investigated. An unusual chromatographic behavior of arsenous acid was observed when tartaric acid was used as mobile phase.
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    URL: http://dx.doi.org/10.1007/BF02466529
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    Retention study on silica gel in high-temperature liquid chromatography (HTLC) (1998)
    Springer
    Chromatographia 47 (1998), S. 278-284 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; High-temperature columns ; Retention behavior ; Column equilibration ; Bilayer formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Retention volumes (V N) of different kinds of test compound have been measured on silica gel as a function of column temperature (T) in the range 20 to 210°C.n-Heptane and mixtures ofn-heptane and polar modifiers were used as mobile phases. With nC7 and nC7-1,4-dioxane mixtures, there was a good linear relationship between InV N and 1/T for column temperatures above 100 °C. When more polar modifiers such as butanol, ethanol and acetic acid were used, ‘N’-shaped curves were obtained for the plots of InV N against 1/T. Possible explanations of this retention behavior have been proposed on the basis of related studies and common physical chemistry relationships. Column equilibration time after alteration of water content or column temperature is greatly reduced at elevated temperatures. This will benefit the application of LSC on silica gel.
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    Highly selective antibody-mediated extraction of isoproturon from complex matrices (1998)
    Springer
    Chromatographia 47 (1998), S. 453-456 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Affinity chromatography ; Selectivity and capacity ; Isoproturon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary For the analysis of pesticides such as isoproturon in complex matrices the rate determining step is sample preparation. A novel solid-phase extraction system for isoproturon based on antibody mediated extraction has been developed. The isoproturon can be retained while the immuno-extraction column is washed with phosphate buffered saline and eluted using phosphate buffered saline/ethanol at low pH. The column can preconcentrate isoproturon from up to at least 1000 mL water and elute in 1 mL. Quantitative recovery of isoproturon from water, plasma and urine can be obtained and the proposed water assay can detect as low as 50 ng L−1 with a 50 mL sample, or 5 ng L−1 with a 1 L sample.
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    URL: http://dx.doi.org/10.1007/BF02466480
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    Porous copolymer of the methacrylic ester of dihydroxydiphenylmethane diglycidyl ether and divinylbenzene as an HPLC packing (1998)
    Springer
    Chromatographia 47 (1998), S. 509-514 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Porous copolymers with hydroxyl groups ; Chemical modification of phases ; Selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Dimethyldichlorosilane has been used to deactivate the hydroxyl groups present in the skeleton of the porous polymer formed from the methacrylic ester ofp, p′-dihydroxydiphenylmethane diglycidyl ether and divinylbenzene. The influence of chemical modification of the copolymer on its chromatographic behavior has been studied. The retention indices of five homologous series and test compounds were calculated to determine the selectivity of the packings.
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    Analysis of anka pigments by liquid chromatography with diode array detection and tandem mass spectrometry (1998)
    Springer
    Chromatographia 47 (1998), S. 529-536 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Thin layer chromatography ; Mass spectrometry detection ; Anka pigments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Anka is withMonascus sp. fermented rice, which shows a purplish red color. On rice grainsMonascus purpureus DSM 1379 synthesized four anka pigments. Through extraction of anka with n-hexane and methanol in succession and through repeated crystallizations from absolute ethanol anka pigments were crystallized into two fractions: organge anka pigments (rubropunctatin and monascorubrin) and yellow anka pigments (monascin and ankaflavin). The treatment of two organge anka pigments with aqueous ammonia solution gave red nitrogen analogues (rubropunctatamine and monascorubramine). The above six pigments were separated into each pigment by two dimensional thin layer chromatography (TLC) or high performance liquid chromatography (HPLC). HPLC-atmospheric pressure chemical ionization-tandem mass spectrometry (HPLC-APCI-MS-MS) and direct probe mass spectrometry (MS) were used to identify these pigments. HPLC-diode array detector (HPLC-DAD) was used to determine UV-VIS spectra of pigments. Pigments were analyzed with HPLC under the following conditions: C18 column, acetonitrile/water (80∶20, v/v), 0.5 mL min−1, 233 nm.
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    Determination of nalbuphine hydrochloride, methylparaben, and propylparaben in nalbuphine hydrochloride injection by high performance liquid chromatography (1998)
    Springer
    Chromatographia 47 (1998), S. 515-522 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; 4,5-Epoxymorphinan ; Nalbuphine hydrochloride injection ; Stability assays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A stability-indicating liquid chromatographic method has been developed for the determination of nalbuphine hydrochloride, methylparaben, and propylparaben in nalbuphine hydrochloride injection. Reversed-phase chromatography was carried out using a mobile phase containing 0.05 % trifuoroacetic acid, acetonitrile, and tetrahydrofuran. Quantitation was achieved with UV detection at 280 nm. Validation data for linearity, accuracy, precision, specificity, and robustness are presented. The chromatographic system resolves nalbuphine from synthetic impurities and degradation products.
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    URL: http://dx.doi.org/10.1007/BF02467488
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    LC phases improve, but not all assays do: Metformin bioanalysis revisited (1998)
    Springer
    Chromatographia 47 (1998), S. 542-546 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Metformin analysis ; Stationary phase variability ; Validation of methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Two assay methods for the antidiabetic metformin, one developed and validated in 1990 and one developed and validated in 1996, are compared. The first method, using an octadecyl phase and an ion pairing agent in the eluent, could not be reproduced some five years later, but another method, using a phenyl phase and no ion pairing agent, could be successfully applied. This paper shows that the retention mechanism of the positively charged analyte is not due to ion-pair formation, as originally assumed, but to interaction with free silanol groups in the LC phase. It is suggested that the number of free silanol groups in octadecyl phases was strongly reduced between 1990 and 1996, whereas for phenyl phases this was not the case. For the second method, validation results on linearity, specificity, accuracy, precision, recovery and stability as well as application of the method to samples from a clinical trial are shown. The validated calibration range is from 20.0 to 2000 ng.mL−1, with accuracy (bias) and precision (coefficient of variation) being below 15% at all levels. Using automated solid-phase extraction for sample preparation, a sample throughput of typically 100 per day can be achieved.
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    URL: http://dx.doi.org/10.1007/BF02467492
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    The use of an optimized RP-HPLC system as a molecular probe in QSPR studies of selected lipid classes (1998)
    Springer
    Chromatographia 47 (1998), S. 643-648 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Quantitative structure retention relationships ; Quantitative structure properties relationships ; Phospholipids ; Molecular probe
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The results of this study show that an optimized RP-HPLC system, in conjunction with molecular mechanics, can be used as a molecular probe to study both configuration and conformation of molecular species of selected phospholipid classes. Specifically, for phosphatidylcholine 18∶0/16∶0, stearic acid is attached to thesn-1 position and palmitic acid is attached to thesn-2 position of the glycerol backbone, for phosphatidylcholine with two monounsaturated fatty acids, the monounsaturated fatty acid attached to thesn-1 position can fold itself backwards on itself, thus allowing van der Waals interaction. Furthermore, it was found in the retention modelling that configurational descriptors alone did not suffice but had to be augmented with conformational descriptors. Nonlinearities were also detected, which could be handled by using a hybrid neural network-PLS regression strategy.
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    URL: http://dx.doi.org/10.1007/BF02467447
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    Separation of lansoprazole enantiomers in human serum by HPLC (1998)
    Springer
    Chromatographia 47 (1998), S. 171-175 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Lansoprazole ; Enantiomers ; Human serum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new and simple HPLC method is described for the separation and quantitative determination of the (+)-and (−)-enantiomers of lansoprazole. The analytes were extracted from serum as previously described for whole lansoprazole [K. Borner, Chromatographia 45, 450–452 (1997)]. The enantiomers were separated by chromatography on a CHIRAL-AGPR column which contained covalently bound acid α1-glycoprotein as chiral selector. In the pure drug the (−)/(+) ratio was 0.99:1.01. In serum of twelve human volunteers the concentration of the (−)-enantiomer was 3 to 5 times higher than that of the (+)-enantiomer. Both enantiomers differ remarkably in their pharmacokinetics.
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    URL: http://dx.doi.org/10.1007/BF02466577
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    Determination of eleven priority EPA phenolics at ng L−1 levels by on-line solid-phase extraction and liquid chromatography with UV and electrochemical detection (1998)
    Springer
    Chromatographia 47 (1998), S. 176-182 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Electrochemical detection ; Phenolics in water ; On-line preconcentration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The eleven priority, EPA phenolic pollutants were determined by liquid chromatography followed by two detectors in series; UV and electrochemical. Three different adsorbents, Envi-Carb (a carbon black) and two functionalized polymeric resins, Bond Elut PPL and another synthesized in our laboratory with an ocarboxybenzoyl moiety, were compared for solid-phase extraction (SPE) to detect lower concentrations of the eleven phenolics in natural waters. Higher recoveries were obtained using the functionalized polymeric adsorbents compared with Envi-Carb. When real samples were analysed, the synthetic adsorbent gave lower interference than Bond Elut PPL and phenol was determined at low levels with no humic and fulvic acid inter-ference when Na2SO3 was added. The linearity range for most compounds in tap water was 0.05–20 μg L−1 and the limits of detection were 〈35 ng L−1. Repeatability and reproducibility between days for real samples spiked at 0.1 μg L−1, expressed as relative standard deviation, were 〈8% and 10%, respectively.
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    URL: http://dx.doi.org/10.1007/BF02466578
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    The use of mobile phase pH and column temperature to reverse the retention order of enantiomers on chiral-AGP® (1998)
    Springer
    Chromatographia 47 (1998), S. 189-196 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Experimental design ; Mosapride ; Reversal of retention order ; Effect of pH and column temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Enantiomeric separation of mosapride and a structurally related compound was performed using chiral chromatography and experimental design. Unique effects of mobile phase pH and column temperature made it possible to control the elution order of the enantiomers when using Chiral-AGP as the solid phase. At a low mobile phase pH (〈6) the (R)-enantiomer of mosapride elutes before the (S)-form whereas the (S)-enantiomer elutes first at a high mobile phase pH (〉6). By using a mobile phase pH around 6, the column temperature could also be used to control the elution order of the enantiomers of mosapride. Similar effects of mobile phase pH and column temperature were obtained for the enantiomers of a structurally related compound, a metabolite (M1). Isocratic chromatographic systems made it possible to determine enantiomeric impurities less than 0.1% in the respective enantiomer of mosapride. The enantiomers of mosapride as well as the enantiomers of M1 could easily be separated simultaneously using Chiral-AGP and a simple gradient elution.
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    URL: http://dx.doi.org/10.1007/BF02466580
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    HPLC determination of colistin and aminoglycoside antibiotics in feeds by post-column derivatization and fluorescence detection (1998)
    Springer
    Chromatographia 48 (1998), S. 32-36 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Post-column derivatization ; Feeds ; Aminoglycoside antibiotics ; Colistin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Reversed-phase, HPLC methods employing post-column derivatization and fluorescence detection were developed for the determination of the peptide colistin and four aminoglycoside antibiotics in feeds. Extraction of the analytes was by sonication and shaking with dilute hydrochloric acid. Post-column derivatization was performed using orthophtaldialdehyde-2-mercaptoethanol chemistry. Assay of colistin was by using an acetonitrile-aqueous sodium sulphate-triethylammonium phosphate (pH 2.8) eluent. Aminoglycoside antibiotics:amikacin, kanamycin, gentamycin and neomycin were analyzed using a tetrahydrofuran-aqueous sodium sulphate-sodium pentanesulphonate-acetic acid mobile phase. The method was also applied to some pharmaceutical preparations. Preliminary results showed that the method can be adapted for the assay of the above antibiotics in meat and animal serum for residue and pharmacokinetic studies.
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    URL: http://dx.doi.org/10.1007/BF02467512
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    High-Performance liquid chromatographic separation of enantiomers of unusual amino acids possessing cycloalkane or cycloalkene skeletons on a chiral crown ether containing stationary phase (1998)
    Springer
    Chromatographia 48 (1998), S. 20-26 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Crownpak CR(+) Column ; Cyclic β-Amino Acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Direct reversed-phase high-performance liquid chromatographic methods were developed for the separation and identification of the enantiomers of mono- and bicyclic racemic β-amino acids:cis- andtrans-2-aminocyclopentane-1-carboxylic acids,cis- andtrans-2-aminocyclohexane-1-carboxylic acids,cis- andtrans-2-amino-4-cyclohexene-1-carboxylic acids,diendo- anddiexo-3-aminobicyclo[2.2.1]heptane-2-carboxylic acids anddiendo- anddiexo-3-amino-5-bicyclo[2.2.1]heptene-2-carboxylic acids. Enantioseparation was carried out by the application of a chiral stationary phase, Crownpak CR(+). The conditions of separation were optimized by changing the temperature, the flow rate and the pH of the mobile phase.
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    URL: http://dx.doi.org/10.1007/BF02467510
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    Enantiomeric separation of unusual secondary aromatic amino acids (1998)
    Springer
    Chromatographia 48 (1998), S. 53-58 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Gas chromatography ; Enantiomeric separation ; Chiral derivatization ; Unusual secondary aromatic amino acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary High-performance liquid chromatographic and gas chromatographic methods were developed for the separation of unusual secondary aromatic amino acids. Amino acids containing 1,2,3,4-tetrahydroisoquinoline, 1,2,3,4-tetrahydronorharmane-1-carboxylic acid and 1,2,3,4-tetrahydro-3-carboxy-2-carboline moieties were synthetized in racemic or chiral forms. The high-performance liquid chromatography was carried out either on a teicoplanin-containing chiral stationary phase or on an achiral C18 column. In the latter case the diastereomers of the amino acids formed by precolumn derivatization with the chiral reagents 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl isothiocyanate or 1-fluoro-2,4-dinitrophenyl-5-L-alanine amide were separated. The gas chromatographic analyses were based on separation on a Chirasil-L-Val column.
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    URL: http://dx.doi.org/10.1007/BF02467516
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    HPLC analysis of basic organic compounds in a multi-component ion-interaction system: A mechanistic study (1998)
    Springer
    Chromatographia 47 (1998), S. 493-500 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-interaction chromatography ; Basic organic compounds ; Diamine modifiers ; Retention mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Reversed-phase HPLC separations of basic compounds have been optimized by use of mobile phases containing 1,8-diaminooctane (DAO) as amine modifier and heptanesulfonate as counter-ion. Such studies have demonstrated the high resolution and selectivity of this chromatographic system compared with mobile phases prepared with the more widely used primary amines. With the aim of clarifying the retention mechanism involved, three sets of compounds with different structures and properties were analyzed: sulfamidics and trimethoprim, aromatic diamines and aminophenols, and a standard mixture of lipophilic basic drugs. The conditions investigated were: diaminoalkane modifier concentration, diaminoalkane modifier alkyl-chain length, nature and concentration of the counter-ion, pH of the mobile phase, concentration of the organic modifer, and the nature of the stationary phase as characterized by percentage carbon loading. Analysis of chromatographic behavior as a function of the chromatographic conditions has enabled the proposal of a mechanism of retention of the three classes of compounds.
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    URL: http://dx.doi.org/10.1007/BF02467485
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    Problems in the analysis of propofol in blood when protein precipitation is used in sample preparation (1998)
    Springer
    Chromatographia 47 (1998), S. 523-528 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Propofol in blood ; Precipitation procedure ; Drug co-precipitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Propofol (2,6-diisopropylphenol) is one of a group of intravenously administered hypnotic agents enabling easy inducement of sleep. Increasingly wider application of this drug in anaesthesiology has led to increasing demands for its precise and reliable analysis in the physiological fluids and tissues of man. The identification of problems in the determination of propofol seems to be essential. This paper deals with difficulties of propofol analysis in blood by HPLC when protein precipitation is used in sample preparation. The data obtained show that introduction of large amounts of fluids (for example electrolytes or blood-substitutes) into the blood, for example during long surgical operations, can significantly influence the results from propofol analysis.
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    URL: http://dx.doi.org/10.1007/BF02467489
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    High performance liquid chromatography method for the determination of doxycycline in human plasma (1998)
    Springer
    Chromatographia 47 (1998), S. 547-549 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Doxycycline ; Human plasma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple, low-cost, sensitive and selective HPLC method was developed for the determination of doxycycline in human plasma. The method has a detection limit of 0.008 μg mL−1 and a limit of quantification of 0.02 μg mL−1. Calibration curves were linear over a large dynamic range, namely within 0.02–5.0 μg mL−1, which allowed accurate determination of doxycycline peak levels in human plasma after administration of 50–200 mg tablets and also the low plasma levels obtained 72 hours after drug administration.
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    URL: http://dx.doi.org/10.1007/BF02467493
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    Determination of triacylglycerol composition of idiazabal cheese (1998)
    Springer
    Chromatographia 47 (1998), S. 579-586 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Column liquid chromatography ; Ewe's cheese ; Triacylglycerols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Triacylglycerols from Idiazabal cheese fat were analysed by high-performance liquid chromatography (LC) with a non-linear gradient of acetone in acetonitrile and a light-scattering detector. Molecular species of triacylglycerols were predicted by a simple and a multiple linear regression analysis of logk of the LC peaks and molecular variables such as equivalent carbon number of the possible triacylglycerol, chain length and number of double bonds of each fatty acid of the triacylglycerol. Predicted results were confirmed by gas chromatographic analysis of the fatty acids in the LC peaks. The main triacylglycerols of Idiazabal cheese fat contained butyric acid, butyroyl-dipalmitin, butyroyl-myristoyl-palmitin and butyroyl-palmitoyl-olein. The most abundant triacylglycerols were those with even partition numbers of 36, 34 and 38.
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    URL: http://dx.doi.org/10.1007/BF02467499
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    Rapid determination of carbaryl and 1-naphthol at ppt levels in environmental water samples by automated on-line SPE-LC-DAD-FD (1998)
    Springer
    Chromatographia 47 (1998), S. 596-600 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; On-line trace-enrichment ; Environmental water samples ; Trace carbaryl analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A fully automated method, based on on-line solid phase extraction (SPE) then liquid chromatography with diode-array and fluorescence detection, has been developed for the trace-level determination of carbaryl and 1-naphthol, its primary transformation product, in environmental water samples. By means of rapid enrichment on a 30 mm×4 mm i.d. 10-μm ODS pre-column, using a 10-mL water sample, before LC determination both compounds were recovered satisfactorily from different environmental water samples spiked at various concentrations (0.05–10 μg L−1). Average recoveries were between 93 and 102% with coefficients of variation between 1 and 4%; detection limits as low as 10 and 50 mg L−1 (ppt) were estimated for carbaryl and 1-naphthol, respectively. With this small sample volume, sample throughput was up to 30 samples per day. A carbaryl degradation study was performed by spiking a surface-water sample at 2 μg L−1. After 15 days 80% of the carbaryl was degraded and the presence of 1-naphthol was confirmed by means of its UV spectrum.
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    URL: http://dx.doi.org/10.1007/BF02467502
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    Isolation and characterization of 3,5,6-trihydroxy-carotenoids from petals ofLilium tigrinum (1998)
    Springer
    Chromatographia 48 (1998), S. 27-31 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Lilium tigrinum ; Carotenoids ; Xanthins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Reinvestigation by HPLC of the petals ofLilium tigrinum and the isolation of some minor compounds is reported. Using HPLC-controlled, preparative-column chromatography, 5,6-diakarpoxanthin (6), 6-epikarpoxanthin (2), 5,6-diacapsokarpoxanthin (8), and 9Z-antheraxanthin (9Z-13) were isolated and characterized. Based on spectroscopic data the absolute configurations of6 and8 were identical with those originating from paprika, thus the 5,6-diakarpoxanthin (6) and 5,6-diacapsokarpoxanthin (8) have the 3S, 5S, 6S configuration and 6-epikarpoxanthin (2) has the 3S, 5R, 6S configuration.
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    URL: http://dx.doi.org/10.1007/BF02467511
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    Chemical removal of humic substances interfering with the on-line solid-phase extraction—Liquid chromatographic determination of polar water pollutants (1998)
    Springer
    Chromatographia 48 (1998), S. 231-236 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; On-line preconcentration ; Humic substances ; Polar pollutants in water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Different methods for removing interference by humic substances in the analysis of polar pollutants have been compared in the analysis of environmental water by solid-phase extraction (SPE) with a chemically modified polymeric resin coupled on-line to liquid chromatography with UV detection. The methods were based on the use of chemical reagents. The best method was found to be addition of sodium sulphite to humic-containing water before SPE. The appropriate amount of sulphite depends on the amount of humic substances dissolved in the sample—for analysis of 50 mL tap and Ebro river water, respectively, 250 μL and 500 μL 10 % Na2SO3 solution had to be added. In both cases, the recovery values after chemical treatment were similar to those when a Milli-Q-quality water standard was analysed.
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    URL: http://dx.doi.org/10.1007/BF02467676
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    Determination of ketorolac enantiomers in plasma using enantioselective liquid chromatography. Application to pharmacokinetic studies (1998)
    Springer
    Chromatographia 48 (1998), S. 203-208 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ketorolac in plasma ; Enantiomer separation ; Pharmacokinetic studies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A direct HPLC method for quantification of the (R) and (S) enantiomers of ketorolac in human plasma for pharmacokinetics studies has been developed. Naproxen sodium [S(+) enantiomer] was used as an internal standard. Plasma samples (1 mL) were vortexed for 30 sec with methyltert-butyl ether, followed by centrifugation at 2000 g for 8 min. The aqueous phase was acidified (pH 1) by adding 1 mL of 2N HCl and back-extracted with 5 mL methyltert-butyl ether. The organic phase was evaporated, and the residue was dissolved in 200 μL of mobile phase. 25 μL were chromatographed on a α1-acid glycoprotein column (Chiral-AGP, 100×4 mm I.D.), using a mobile phase with 8.5% propan-2-ol in phosphate buffer (0.09M NaH2PO4.H2O, 0.01M Na2HPO4, 0.002M Dimethyloctylamine; pH 5.5). Calibration range was 20–20000 ng mL−1 for (R)- and (S)-ketorolac. The LOQ was 5 ng mL−1 for both enantiomers. The sensitivity could be extended to 1 ng mL−1 with the same precison by increasing the injection volume to 100 μL. The method is reproducible, accurate, and stereospecific. The inter-assay and intra-assay CVs were 〈11.40% and 〈9.30% for (R)- and (S)-ketorolac respectively. Under the conditions employed, no racemization was observed.
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    URL: http://dx.doi.org/10.1007/BF02467672
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    Optimisation of mobile phase pH in liquid chromatography. Application to fluorimetric detection of series of quinolones (1998)
    Springer
    Chromatographia 48 (1998), S. 251-257 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Mobile phase optimisation ; Fluorimetric detection ; Quinolones ; Dissociation constants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The dissociation constants of several quinolones in a 7% acetonitrile-water mixture are determined. A model describing the effect of pH on the retention of quinolones by an octadecylsilica stationary phase with a 7% acetonitrile-water mobile phase is proposed. The model uses pH values in the mobile phase instead of pH values in water and takes into account the effect of activity coefficients. Fluorescence of quinolones in the mobile phase is studied, and a chromatographic separation with fluorimetric detection is established. Detection limits for the proposed method range from 3 to 12 μg·L−1.
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    URL: http://dx.doi.org/10.1007/BF02467679
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