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  • 1
    ISSN: 1520-6882
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 531-538 
    ISSN: 0935-6304
    Schlagwort(e): Capillary isotachophoresis ; capillary electrophoresis ; column-coupling electrophoresis ; enantiomers ; chiral ; amino acids ; tryptophan ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---The ability of capillary zone electrophoresis (CZE) coupled on-line with capillary isotachophoresis (ITP) sample pretreatment in the column-coupling capillary electrophoresis equipment to separate trace enantiomers present in samples of complex ionic matrices and enantiomers present in their mixtures at significantly differing concentrations has been studied. Enantiomers of 2,4-dinitrophenyl labeled norleucine (DNP-Nleu) and tryptophan enantiomers were employed as model analytes in this work while urine and mixtures of tryptophan enantiomers of differing concentrations served as model samples. Experiments performed with urine samples spiked with the DNP-Nleu racemate at sub-μmol/L concentrations demonstrated excellent sample pretreatment capabilities of ITP (concentration of the analytes, in-column and post-column sample clean up) when coupled on-line with chiral CZE separations. In the CZE separations of enantiomers present in the samples at trace concentrations the sample pretreatment could be performed in both achiral and chiral ITP electrolyte systems. The use of a chiral electrolyte system was found to be essential in the ITP pretreatment of the samples containing the enantiomers at very differing concentrations. For example, a 2×10-7 mol/L concentration of L-tryptophan could be detected in the CZE separation stage of the ITP-CZE combination in samples containing about a 104 excess of D-tryptophan only when the ITP pretreatment was carried out in the electrolyte system providing the resolution of enantiomers (α-cyclodextrin served for this purpose in the present work). A post-column ITP sample clean up was found effective in enhancing the destacking rate of the trace enantiomer in the CZE stage when the migration configuration of the enantiomers was less favorable (the trace constituent migrating behind the major enantiomer).
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Electrophoresis 18 (1997), S. 260-267 
    ISSN: 0173-0835
    Schlagwort(e): Preparative capillary isotachophoresis ; Capillary zone electrophoresis ; Nitrophenols ; Water analysis ; Isotachophoretic sample pretreatment ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Preparative capillary isotachophoresis (ITP) operating in a discontinuous frationation mode was studied as a sample pretreatment technique for capillary zone electrophoresis (CZE) trace analysis of a group of ten nitrophenols. Different separation mechanisms employed by these capillary electrophoresis techniques made possible a group isolation of the studied analytes by ITP while their CZE resolutions based on differences in the interactions with polyvinylpyrrolidone (PVP) provided suitable conditions for a final analytical evaluation. Experiments with model and practical water samples revealed high and reproducible recovery rates of the ITP pretreatment for nitrophenols when sample loadability limits of the preparative ITP equipment were met. A main disadvantage of the studied ITP-CZE combination was an inefficient use of the pretreated sample as only 0.5% of the fraction containing nitrophenols was used in the final CZE step. Despite these limitations associated with the CZE sample injection, the concentration limit of detection (LOD) for nitrophenols in practical water samples could be reduced to 2-8 ppb concentrations (photometric absorbance detector operating at a 254 nm wavelength) when 200 μL sample volumes were taken for the ITP pretreatment. This was accompanied by an efficient sample clean-up as no other trace ionic constituents originating from the samples were detected on CZE.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Electrophoresis 17 (1996), S. 1890-1897 
    ISSN: 0173-0835
    Schlagwort(e): Capillary zone electrophoresis ; Inorganic aninos ; Conductivity detection ; Hydrodynamically closed separation system ; Water analysis ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: A carrier electrolyte system for capillary zone electrophoresis (CZE) resolving chloride, bromide, iodide, fluoride, nitrite, nitrate, sulfate, and phosphate in a hydrodynamically closed separation compartment is described. The carrier electrolyte combines the effects of pH, polyvinylpyrrolidone (PVP) and the counterionic constituent on the effective mobilities of the anions. In 300 μm ID capillary tubes made of fluorinated ethylene-propylene copolymer (FEP), and with detection of analytes with the aid of an alternating current conductivity detector, detection limits in the range of 3-10 ppb could be achieved for 200 nL sample volumes. The separation efficiencies were in the range of 1.5-2.5 × 105 theoretical plates per meter for an adequate sample load. The reproducibility was evaluated for two concentration levels. For concentrations close to the limits of quantitation (50-120 ppb), the RSD values ranged from 1.5-12.6%, with the highest scatter for fluoride and phosphate. The RSD values were in the range of 0.4-1.5% for 300-1200 ppb concentrations of the anions. Typical analysis times were 2-5 min, depending on the anion species. A series of water samples (drinking, river, rain) was used to assess the practical applicability of the CZE method. The method is a suitable alternative for the determination of both anionic macro- and microconstituents in water with a good overall selectivity.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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