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  • Column liquid chromatography  (12)
  • Surface physics, nanoscale physics, low-dimensional systems
  • 1990-1994  (12)
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  • 1
    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
    Standort Signatur Erwartet Verfügbarkeit
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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
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    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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  • 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
    Use of membrane extraction disks for on-line trace enrichment of organic compounds from aqueous samples (1990)
    Springer
    Chromatographia 29 (1990), S. 415-418 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Trace enrichment ; Membrane extraction disks ; Triazine herbicides ; 2,3,4-Trichlorophenol
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Membrane extraction disks have been recently introduced for the solid-phase extraction of organic compounds from aqueous samples. The material consists of alkyl-modified silica particles enmeshed in an inert PTEE matrix. Aqueous samples containing polar pesticides and herbicides, are preconcentrated on-line from acidic solutions on membrane extraction disks containing immobilized octadecyl-modified silica and analyzed with an isocratic liquid chromatographic system using PLRP-S as the stationary phase and aqueous acetonitrile mixtures (pH 3) as the eluent. Data on the lifetime and the dimensions of the preconcentration disks, and the efficiency and the repeatability of the procedure are reported. For 10 ml samples, the detection limits of the analytes atrazine, simazine and 2,3,4-trichlorophenol in tap water are 0.1–1 ppb.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02261387
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  • 6
    Digitale Medien
    Digitale Medien
    On-line monitoring of fermentation processes by ultrafiltration and column liquid chromatography (1992)
    Springer
    Chromatographia 33 (1992), S. 525-532 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Ultrafiltration ; Fermentation monitoring ; Sugars
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary An automated on-line monitoring system for low-molecular-weight compounds (e.g. sugars) during fermentation processes is described. The applicability of cross-flow ultrafiltration, coupled on-line with high-performance liquid chromatography, is evaluated. Various detection modes for the determination of the test compounds lactose, glucose and fructose) in a complex fermentation broth are compared. In addition, the influence of some system parameters on the performance of several ultrafiltration modules for the removal of cellular and macromolecular broth constituents is investigated. A method for the fully automated determination of sugars during anE. coli batch culture in a brain-heart infusion medium is presented. With the present system five analyses can be performed every hour, using only 35μl of sample, without significant deterioration of the ultrafiltration process. Contamination by external micro-organisms was not observed and good correlation with an off-line method was found.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02262243
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  • 7
    Digitale Medien
    Digitale Medien
    Immunoaffinity precolumn for selective sample pretreatment in column liquid chromatography: Immunoselective desorption (1991)
    Springer
    Chromatographia 31 (1991), S. 469-477 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Immunoaffinity precolomn ; Oestrogens ; Bioanalysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02262391
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  • 8
    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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  • 9
    Digitale Medien
    Digitale Medien
    Determination of polar pollutants in water using an on-line liquid chromatographic preconcentration system (1991)
    Springer
    Chromatographia 32 (1991), S. 445-452 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; On-line preconcentration ; Polar pollutants ; Water (tap and surface)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary An isocratic column liquid chromatographic system with UV absorbance detection at 230 nm has been developed for the rapid trace-level determination of a large number of polar pollutants in water. The systems contains two precolumns, in series, which are packed with a styrenedivinylbenzene (PLRP-S) polymer. The second precolumn is also loaded with sodium dodecylsulphate before use. Each precolumn is combined with a PLRP-S analytical column, and aqueous acetonitrile mixtures (pH 3) are used for the separation of neutral as well as acidic and basic pollutants. With 10-ml water samples the detection limits for all analytes, in tap water, are in the low to sub μg/l range. Relevant analytical data are reported and the advantage of using a dodecylsulphate-loaded precolumn over a cation-exchange precolumn is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02327976
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  • 10
    Digitale Medien
    Digitale Medien
    Trace enrichment of polar pollutants from water and the influence of humic substances (1993)
    Springer
    Chromatographia 37 (1993), S. 13-19 
    Details
    ISSN: 1612-1112
    Schlagwort(e): Column liquid chromatography ; Polar pollutants in water ; On-line trace enrichment ; Humic substances
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A practical liquid chromatographic early-warning system for polar pollutants in water ought to have detection limits at a level below a microgram per litre. Using ultraviolet absorbance detection this normally necessitates trace enrichment of the samples. In this study ten different sorbents have been tested with respect to their enrichment capacity. The hydrophobic polymeric PLRP-S material, in combination with a C-18 modified analytical column, proved to be the best choice. The influence of humic substances, present in surface water, was also studied. Lowering of the sample pH, resulted in a significant increase in the interferences due to the humic substances.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02272181
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