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  • 1
    Digitale Medien
    Digitale Medien
    Theoretical models for electrodialytic sample treatment in trace analysis by liquid chromatography (1994)
    Springer
    Chromatographia 39 (1994), S. 460-468 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Electrodialytic sample treatment ; Computer models ; Analyte enrichment
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Basic considerations for analyte enrichment and recovery obtainable by electrodialysis as a sample treatment method are given. Equations are derived which describe the dependence of the concentration profiles of ionic compounds on the electric field strength in a set-up with stagnant donor and acceptor solutions. It is shown that analyte recovery increases when less ion-selective membranes are used in the electrodialysis cell. Computer models are used to estimate the analyte enrichment for a flowing donor (sample) and a stagnant acceptor phase. About 10-fold enrichment can be obtained in an electrodialytic sample treatment system within 20 min under maximum current conditions. A compromise has to be found between analyte recovery and the donor (sample) flow rate.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02278763
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  • 2
    Digitale Medien
    Digitale Medien
    Electrodialytic sample treatment coupled on-line with high-performance liquid chromatography (1990)
    Springer
    Chromatographia 30 (1990), S. 361-366 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Electrodialytic sample treatment ; On-line coupling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary An electrodialytic sample treatment method coupled on-line with high-performance liquid chromatography (EDIST-HPLC) is discussed in this paper. The performance of EDIST as a function of the donor-phase (sample solution) flow rate, the voltage applied over the electrodialysis block, and the time of dialysis has been studied using the basic drug ephedrine as a model compound. Enrichment of the analyte by a factor of 10–20 was possible. The determination of human plasma spiked with ephedrine is briefly discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02328498
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  • 3
    Digitale Medien
    Digitale Medien
    Zone electrophoretic sample treatment coupled on-line with column liquid chromatography for the determination of basic and acidic compounds in biological samples (1992)
    Springer
    Chromatographia 34 (1992), S. 581-588 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Zone-electrophoretic sample treatment ; Basic and acidic compounds ; Biological samples
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A modified valve arrangement for zone-electrophoretic sample treatment (ZEST)-which is coupled on-line with column liquid chromatography — is used to pretreat biological (plasma) samples. Carry-over of plasma proteins depends on the pH of the electrophoresis buffer. The determination of propranolol, metoprolol, cromolyn and salicylic acid demonstrates that both basic and acidic analytes can be isolated from the plasma matrix with high selectivity. Analogous piperazines, with different protein binding properties, were used to study the influence of protein binding on the recovery. It is shown that high protein can cause a decreased recovery.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02269867
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  • 4
    Digitale Medien
    Digitale Medien
    A new valve for zone-electrophoretic sample treatment coupled on-line with high performance liquid chromatography (1990)
    Springer
    Chromatographia 29 (1990), S. 217-222 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Sample treatment ; Zone electrophoresis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The design of a new valve arrangement for zone-electrophoretic sample treatment (ZEST) coupled online with high performance liquid chromatography is described. Characteristics of this valve, such as the internal heat development as a function of the current, have been investigated. By using quinidine and desipramine as model compounds it is shown that charged compounds can be isolated from biological samples, in about 15 min, with high selectivity. The carry-over of proteins to the analytical column has been compared with the carry-over using a pre-column sample clean-up method. The detection limits of quinidine and hydroquinidine (50 ng/ml), using zone-electrophoretic sample treatment coupled with column liquid chromatography, are in the same range as with direct injections using pre-columns.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02317907
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  • 5
    Digitale Medien
    Digitale Medien
    Determination of sugars by liquid chromatography and amperometric detection with a cuprous oxide modified electrode (1995)
    Springer
    Chromatographia 40 (1995), S. 684-689 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Sugars ; Amperometric detection ; Chemically modified electrodes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A chemically modified electrode was applied as a working electrode for the amperometric detection of sugars in liquid chromatography. A mixture of cuprous oxide and conductive carbon cement was used as electrode material. Cuprous oxide acted as a catalyst for the oxidation of sugars. Cyclic voltammetry was used to examine the oxidation of the sugars at the electrode surface. The stability and sensitivity of a cuprous oxide/conductive carbon cement (20/80 %, w/w) electrode were tested in flow injection analysis experiments. For liquid chromatography, sugars were separated on an ion-exclusion column with 0.01 M H2SO4 as mobile phase. After the separation, 0.2 M NaOH was added post-column and the sugars were determined at 550 mV vs. Ag/AgCl. Calibration was linear in the range of 10−6·10−3 M with limits of detection of approximately 1·10−6M. The application of the modified electrode for the determination of sugars in fruit beverages and dairy products following chromatographic separation is shown.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02315138
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  • 6
    Digitale Medien
    Digitale Medien
    Reversed-phase liquid chromatography coupled on-line with capillary gas chromatography use of an anion-exchange membrane to remove an ion-pair reagent from the eluent (1995)
    Springer
    Chromatographia 40 (1995), S. 267-271 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Column liquid chromatography ; On-line coupling ; Ion-exchange membrane ; Ion-pair reagent
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02290356
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  • 7
    Digitale Medien
    Digitale Medien
    On-line trace enrichment — column liquid chromatography of polar pollutants in surface water using bifunctional membrane-based extraction-disk cartridges (1994)
    Springer
    Chromatographia 39 (1994), S. 239-245 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Membrane-extraction disks ; On-line trace enrichment ; Polar pollutants ; Surface water
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary An on-line trace-enrichment system, using a bifunctional membrane extraction-disk cartridge, has been combined with a column liquid chromatography separation for the simultaneous determination of basic, neutral and acidic pollutants in surface water. The enrichment device consisted of a specially constructed holder containing both C-18 and cation-exchange disks. The holder can contain up to 25 disks of 0.5 mm thickness and 4.6 mm diameter. Before trace enrichment of 20 ml of surface water (pH 3.0), calcium ions were removed from the sample by means of an oxalic acid precipitation. Desorption of the cartridge was at elevated temperature using reversed-phase gradient elution; detection was performed with a diode-array UV absorbance detector. The detection limits for the test compounds in surface water are typically 0.5–2 μg/l; the calibration graphs are linear from the lower limit of determination up to 50 μg/l.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02274506
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  • 8
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): Column liquid chromatography ; Short-Column LC ; Environmental water samples ; MS-MS detection ; Pesticide degradation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02466637
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  • 9
    Digitale Medien
    Digitale Medien
    Determination of triazine herbicides in surface and drinking waters by off-line combination of liquid chromatography and gas chromatography-mass spectrometry (1992)
    Springer
    Chromatographia 34 (1992), S. 5-13 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Gas chromatography-mass spectrometry ; Water analysis ; Triazine herbicides ; Chemical ionization mass spectrometry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Mass spectra of 12 triazines were obtained by electron impact (EI), positive-ion chemical ionization (PCI) and negative-ion chemical ionization (NCI) using methane and isobutane as reagent gases. EI mass spectrometry is more sensitive than PCI and NCI, although the chemical ionization modes increase selectivity markedly. A pre-column packed with polymer stationary phase was employed to preconcentrate surface and drinking water samples. After desorption of the analytes with ethyl acetate, an aliquot was injected directly into the GC-MS system. Atrazine and simizine were found in these samples at 10–80 ppt levels. The limits of detection for both herbicides were below 10 ppt in drinking water.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02290451
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  • 10
    Digitale Medien
    Digitale Medien
    Application of diode array detectors for solute identification in toxicological analysis (1989)
    Springer
    Chromatographia 28 (1989), S. 341-353 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Diode array detectors (DAD) ; Toxicology ; Automated solute identification
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The possibilities and limitation of automated solute identification via UV/VIS spectroscopy in HPLC are demonstrated and applications in toxicologic analysis are described. A standard isocratic system is used. The influence of various chromatographic parameters on retention time is shown. A retention time window of ±15% is required. In addition to retention time, derived spectral data are calculated (minima and maxima of derivatives, area counts under standardized spectral ranges, absorption at various wavelength) and used for positive solute identification. It is possible to identify solutes with a high degree of certainty in urine and plasma if their concentration is at least 10 ppm.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02261012
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