Capillary zone electrophoresis buffer system

Capillary zone electrophoresis coupled with fast cyclic voltammetric detection was developed by Zhou et al. [27] for the separation and determination of OTC, TC, and CTC antibiotics. All compounds were well separated by optimization of pH and complexation with a boric acid sodium tetraborate buffer. The detection limit using fast on-line cyclic voltammetric detection with Hg-film-microm electrode was 1.5 x 10-6 mol/L for OTC (signal to noise ratio > 2). A continuous flow manifold coupled on-line to a capillary electrophoresis system was developed by Nozal et al. [28] for determining the trace levels of OTC, TC, and DC in surface water samples. 

Capillary zone electrophoresis is another technique which has been used to separate products such as organic acids.26 Separation is based on differences in the mobility of analytes exposed to an electric field. Resolution and separation time in such systems depends on factors including electroosmotic flow (EOF), and a number of approaches for adjusting the EOF have been examined. While some of the approaches (pretreatment of capillaries) are not useful as means of process control, adjusting buffer pH and the electric field27 seem to be possible handles for true feedback control of the separation, although closed-loop operation does not seem to have been attempted. 

Capillary Zone Electrophoresis. The most fundamental approach that involves the use of a fused-silica capillary placed between the two buffer vials so that separation of the sample component occurs after an electric field (voltage) is applied to the system. Separation of the analytes is based on differences in electrophoretic mobility. Only charged compounds, both large and small, can be separated in this format. 

The main separation modes used in CE are capillary zone electrophoresis (CZE), micellar electrokinetic capillary chromatography (MEKC), capillary isotachophoresis, capillary gel electrophoresis, and capillary isoelectric focusing. CZE and MEKC are used most often. CE buffers are generally aqueous-based, though nonaqueous systems are exploited as well, particularly for analytes that are insoluble or sparingly soluble. 

Capillary zone electrophoresis (CZE) is a powerful technique, magnetic in its analytical personality as a result of the simple way diverse analytes can be resolved rapidly and with high efficiency. The attraction is easy to understand—an electrophoretic technique with as much bandwidth as (and complementary to) HPLC and multiple modes of separation available by simply changing the buffer system. Yet within the simple instrumental framework that is, at its root, a power supply, a capillary and a detector, lies the capability to analyze drugs, peptides, carbohydrates, and proteins in sample matrices as simple as buffer or as complex as semm. That power is the magnet that draws people in. 

Schwer, C., Gas, B., Lottspeich, F., and Kenndler, E., Computer simulation and experimental evaluation of on-column sample preconcentration in capillary zone electrophoresis by discontinuous buffer systems, AnaZ. Chem., 65, 2108, 1993. 

In the simplest CZE system with UV detection as background electrolyte (BGE) a Tris buffer of pH 6 was employed with detection at 200 nm, or with 40 mM acetate buffer at pH 4.0 and with detection at 238 nm. l The first conditions were employed for determination of MC in fractions from preparative HPLC with detection limit reported for MC-LR as 3 ppm. For the same purpose also, the second-mentioned conditions were suitable, showing impurity of [D-dsp ]MC-LR in MC-LR samples.Capillary zone electrophoresis with UV detection... 

Figure 4.23 Diagram ofa simple system for capillary zone electrophoresis (CZE, the most commonly used version of CE) using an integrated spectroscopic detector (UV-visible absorption or fluorescence). The example illustrated is set up for analysis of compounds that are cations under the buffer conditions used.

An on-line coupling of capillary electrophoresis or reversed anionic capillary isotachophoresis (CITP) with electrospray ionization mass spectrometry has been described for the separation of monophosphate nucleosides, pyridine, and flavin dinucleotides (87). The combination with CITP gives an enhancement of sample loadability and concentration sensitivity in capillary zone electrophoresis/ mass spectrometry (CZE/MS). MS-compatible buffer systems were developed (trailing electrolyte, 10 mM caproic acid pH 3.4 leading electrolyte, 7 mM HCl/ 13 mM P-alanine pH 3.9). This technique seems to be valuable for the trace analysis of DNA and RNA, e.g., to study radiation-induced DNA damage. 

A mixture of several water-soluble vitamins including calcium pantothenate was recently evaluated by CE by Jegle (83). The sample was analyzed in a 0.02 M sodium phosphate buffer (pH 7) and separated using a three-dimensional capillary zone electrophoresis system (flised-siUca, 50 pm i.d., straight, length to detector 400 mm, total length 485 mm, injection pressure 4.6 sec at 4 kPa, postinjection pressure 4 sec at 40 kPa, polarity positive, voltage 20 kV, capillary temperature... 

The use of CE methods for routine quality control of synthetic or recombinant peptides-proteins necessitates optimization strategies for rapid method development. Ideally, the methods should be simple, fast, and robust. Because capillary electrophoresis in the zone format is the most simplistic, initial efforts should be directed toward the use of a simple buffer system [61]. The high efficiency and reproducibility in protein-pep-tide separations demands that interactions between the analyte and capillary wall be neglible. The use of low-pH buffers generally results in enhanced reproduciblity, and hence ruggedness, as slight variations in the capillary surface will have little impact on the already suppressed EOF. 

Capillary isotachophoresis (CITP) — An electrophoretic separation technique (-> electrophoresis) in a discontinuous -> buffer system, in which the analytes migrate according to their -> electrophoretic mobilities, forming a chain of adjacent zones moving with equal velocity between two solutions, i.e., leading and terminating electrolyte, which bracket the mobility range of the analytes. Ref [i] Riekkola ML, Jonsson jA, Smith RM (2004) Pure Appl Chem 76 443... 

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