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  • 1
    ISSN: 1612-1112
    Keywords: Chemical excitation source ; Chemiluminescence detector ; Chemical band narrowing ; Dansyl derivative ; Serum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A peroxyoxalate chemiluminescence detection system for liquid chromatography is described. The excitation of fluorophores is generated by the reaction of bis-(2,4,6-trichlorophenyl)oxalate or bis(2,4-dinitrophenyl)oxalate and hydrogen peroxide, which are added to the column effluent. The influence of the solvents and the concentrations of the reagents have been investigated. The influence of the flow cell volume on sensitivity and on band broadening have also been studied and a “chemical band narrowing effect” has been observed. Different types of apparatus have been compared for detection of the emitted light. The system has been used for the detection of the dansyl derivative of a drug with a secondary amine functional group in serum samples. The detection limits are in the 1–10pg range.
    Type of Medium: Electronic Resource
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  • 2
    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.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Immunoaffinity precolomn ; Oestrogens ; Bioanalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An automated liquid chromatographic system is described using immunoaffinity precolumns for sample pretreatment. The system consists of a column-switching unit allowing preconcentration from a large volume of sample (e.g. 15 ml of urine) onto an immunoaffinity precolumn (containing polyclonal antibodies immobilized on Sepharose). After sorption, the analytes are desorbed by a mixture of two cross-reacting solutes, followed by reconcentration on a C-18-bonded silica precolumn, and then separation on a C-18-bonded silica analytical column. Using oestrogen steroids as model compounds and UV absorbance detection, the minimum detectable concentration is ca. 200 ng/l with a repeatability of 6–8%. The total analysis time is 45 min which allows the unattended analysis of 30 samples per day. The features of the sample pretreatment method, especially of the immunoselective desorption, are evaluated and the general applicability of the system is discussed.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Reversed-phase system ; On-line post-column extraction ; Electron-capture detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A post-column extraction module has been used for the on-line coupling of conventional-size (4.6mm i.d.) reversed-phase liquid chromatography (PPLC) and electron-capture detection (ECD). Hexane and toluene were used as extraction solvents, while methanol turned out to be preferable to dioxane and acetonitrile as modifier in the aqueous eluent. In this system the ECD behaves as a concentration-sensitive detector. The band broadening in the evaporation interface, which connects the extraction module with the ECD, dominates the total post-column band broadening; it can be reduced to 3–4 sec by directing at least 0.25–0.30 ml/min (i.e. 25–30%) of the extraction solvent to the ECD. Optimal signal-to-noise ratios were observed if 30–60% of the extraction solvent is directed to the ECD. The noise levels are 5–10 times higher than in systems using a direct coupling of normal-phase LC or narrow-bore reversed-phase liquid chromatography to the ECD. Separations of phenylurea herbicides and chlorophenols demonstrate the applicability of the RPLC-extraction module-ECD system.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Column liquid chromatography ; On-line coupling ; Ion-exchange membrane ; Ion-pair reagent
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In order to enable the coupling of reversed-phase liquid chromatography (RPLC) with capillary gas chromatography (GC), the performance of an anion-exchange micromembrane device has been studied to remove the ion-pair reagent methanesulphonic acid from an acetonitrile/water LC eluent. The regenerant in the membrane was tetrabutylammonium hydroxide dissolved in acetonitrile/water, which effects an anion-exchange of methanesulphonate ions for regenerant hydroxide ions. The efficiency of the exchange process was found to be 99.9%. This enabled the direct introduction of the LC eluent, free of ions and with the proper acetonitrile/water ratio, into the GC. The applicability of the on-line LC-micromembrane-GC system has been illustrated for the potential drug eltoprazine, which is quantitatively recovered with a coefficient of variation for standard solutions of 3% at the 150 μg/ml analyte level.
    Type of Medium: Electronic Resource
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