Capillary zone electrophoresis buffers

Capillary Zone Electrophoresis The simplest form of capillary electrophoresis is capillary zone electrophoresis (CZE). In CZE the capillary tube is filled with a buffer solution and, after loading the sample, the ends of the capillary tube are placed in reservoirs containing additional buffer solution. Under normal conditions, the end of the capillary containing the sample is the anode, and solutes migrate toward... 

Diet soft drinks contain appreciable quantities of aspartame, benzoic acid, and caffeine. What is the expected order of elution for these compounds in a capillary zone electrophoresis separation using a pH 9.4 buffer solution, given that aspartame has pJC values of 2.964 and 7.37, benzoic acid s pfQ is 4.2, and the pfQ for caffeine is less than 0. 

Catechin and epicatechin are two flavanols of the catechin family. They are enantiomers. The capillary zone electrophoresis (CE) methods with UV-detection were developed for quantitative determination of this flavanols in green tea extracts. For this purpose following conditions were varied mnning buffers, pH and concentration of chiral additive (P-cyclodextrin was chosen as a chiral selector). Borate buffers improve selectivity of separation because borate can make complexes with ortho-dihydroxy groups on the flavanoid nucleus. 

Indirect UV absorbance detection in capillary zone electrophoresis has been used to analyze sodium alcohol sulfates. Excellent reproducibility was obtained when veronal buffer was used as UV-absorbing background electrolyte [302],... 

Capillary electrophoresis (CE) or capillary zone electrophoresis (CZE) is the technique most often employed in pesticide residue analysis. In its most basic form, free zone electrophoresis, a fused-silica capillary is filled with electrolyte (running buffer or background electrolyte). A potential is applied across the capillary and the cations... 

Gassner, B., Friedl, W., and Kenndler, E., Wall adsorption of small anions in capillary zone electrophoresis induced by cationic trace constituents of the buffer, /. Ckromatogr., 680, 25, 1994. 

Mosher, R. A., The use of metal ion-supplemented buffers to enhance the resolution of peptides in capillary zone electrophoresis, Electrophoresis, 11, 765, 1990. 

Grossman, R D., Wilson, K. J., Petrie, G., and Lauer, H. H., Effect of buffer pH and peptide composition on the selectivity of peptide separations by capillary zone electrophoresis, Anal. Biochem., 173, 265, 1988. 

Green, J. S. and Jorgenson, J. W., Minimizing adsorption of proteins on fused silica in capillary zone electrophoresis by the addition of alkali metal salts to the buffers, /. Chromatogr., 478, 63, 1989. 

Righetti, P.G., Gelfi, C., Perego, M., Stoyanov, A.V., and Bossi, A., Capillary zone electrophoresis of oligonucleotides and peptides in isolectric buffers theory and methodology, Electrophoresis, 18, 2145, 1997. 

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. 

Gotti et al. [42] reported an analytical study of penicillamine in pharmaceuticals by capillary zone electrophoresis. Dispersions of the drug (0.4 mg/mL for the determination of (/q-penicillaminc in water containing 0.03% of the internal standard, S -met hy I - r-cystei ne, were injected at 5 kPa for 10 seconds into the capillary (48.5 cm x 50 pm i.d., 40 cm to detector). Electrophoresis was carried out at 15 °C and 30 kV, with a pH 2.5 buffer of 50 mM potassium phosphate and detection at 200 rnn. Calibration graphs were linear for 0.2-0.6 pg/mL (detection limit = 90 pM). For a more sensitive determination of penicillamine, or for the separation of its enantiomers, a derivative was prepared. Solutions (0.5 mL, final concentration 20 pg/mL) in 10 mM phosphate buffer (pH 8) were mixed with 1 mL of methanolic 0.015% 1,1 -[ethylidenebis-(sulfonyl)]bis-benzene and, after 2 min, with 0.5 mL of pH 2.5 phosphate buffer. An internal standard (0.03% tryptophan, 0.15 mL) was added and aliquots were injected. With the same pH 2.5 buffer and detection at 220 nm, calibration graphs were linear for 9.3-37.2 pg/mL, with a detection limit of 2.5 pM. For the determination of small amounts of (L)-penicillamine impurity, the final analyte concentration was 75 pg/mL, the pH 2.5 buffer contained 5 mM beta-cyclodextrin and 30 mM (+)-camphor-10-sulfonic acid, with a voltage of 20 kV, and detection at 220 nm. Calibration graphs were linear for 0.5-2% of the toxic (L)-enantiomer, with a detection limit of 0.3%. 

In CZE, the capillary, inlet reservoir, and outlet reservoir are filled with the same electrolyte solution. This solution is variously termed background electrolyte, analysis buffer, or run buffer. In CZE, the sample is injected at the inlet end of the capillary, and components migrate toward the detection point according to their mass-to-charge ratio by the electrophoretic mobility and separations principles outlined in the preceding text. It is the simplest form of CE and the most widely used, particularly for protein separations. CZE is described in Capillary Zone Electrophoresis. ... 

For capillary zone electrophoresis (CZE) mass spectrometry coupling, another modification of an ESI interface has been developed. This interface uses a sheath flow of liquid to make the electrical contact at the CZE terminus, thus defining both the CZE and electrospray field gradients. This way, the composition of the electro sprayed liquid can be controlled independently of the CZE buffer, thereby providing operation with buffers that could not be used previously, e.g., aqueous and high ionic strength buffers. In addition, the interface operation becomes independent of the CZE flow rate. [62]... 

Stoyanov, A. V., Gelfi, C., and Righetti, P. G. (1997). Capillary zone electrophoresis of oligonucleotides in isoelectric buffers and against a stationary pH gradient. Electrophoresis 18, 717-723. 

Chiari, M., and Kenndler, E. (1995). Capillary zone electrophoresis in organic solvents-separation of anions in methanolic buffer solutions./. Chromatogr. A 716, 303-309. 

Since all electrophoretic mobility values are proportional to the reciprocal viscosity of the buffer, as derived in Chapter 1, the experimental mobility values n must be normalized to the same buffer viscosity to eliminate all other influences on the experimental data besides the association equilibrium. Some commercial capillary zone electrophoresis (CZE) instruments allow the application of a constant pressure to the capillary. With such an instrument the viscosity of the buffer can be determined by injecting a neutral marker into the buffer and then calculating the viscosity from the time that the marker needs to travel through the capillary at a set pressure. During this experiment the high voltage is switched off. 

CE Lin, WC Lin, WC Chiou, EC Lin, CC Chang. Migration behavior and separation of sulfonamides in capillary zone electrophoresis. I. Influence of buffer pH and electrolyte modifier. J Chromatogr A 755 261-269, 1996. 

Capillary zone electrophoresis is a powerful tool for the separation of water-soluble vitamins, such as nicotinic acid and vitamin C, with high-pH borate or phosphate buffers. Most simultaneous separations have been performed for fat-soluble vitamins, such as vitamins A and E, by MEKC. Here, organic... 

In its simplest form capillary electrophoresis is termed capillary zone electrophoresis . The conditions used in this type of analysis are relatively simple and the mobile phase used consists of a buffer with various additives. Many applications focus on critical separations which are difficult to achieve by HPLC. In many cases it is difficult to explain completely the types of effects produced by buffer additives. 

Hoyt and Sepaniak have used capillary zone electrophoresis to determine procaine in pharmaceuticals as a cation of benzylpenicillin [148]. A benzylpenicillin potassium tablet (250 mg) was treated with 20 mL of a 0.2% phenol solution (the internal standard), and dispersed in water. The solution was diluted to 500 mL, and samples were introduced into the fused silica capillary tube (70 cm x 50 gm) by siphoning. With 10 mM Na2HP04-6mM Na2B407 buffer as the mobile phase, the samples were subjected to electrophoresis at 30 kV (25 to 30 pA), and the emerging analytes detected at 228 nm within 10 minutes. 

Micellar electrokinetic capillary chromatography (MECC), in contrast to capillary electrophoresis (CE) and capillary zone electrophoresis (CZE), is useful for the separation of neutral and partially charged species [266,267]. In MECC, a surfactant, usually sodium dodecyl sulfate (SDS), is added to the buffer solution above its critical micellar concentration to form micelles. Although SDS is certainly the most popular anionic surfactant in MECC, other surfactants such as bile salts have proved to be very effective in separating nonpolar analytes that could not be resolved using SDS [268]. 

A determination of PQQ by capillary zone electrophoresis was also developed <2000JCH(739)101>. The optimal separation conditions were a 50mM /3-alanine HCl pH 3.0 buffer, an applied voltage of 25 kV (negative polarity), and a temperature of 25 °C. The linear detection range for concentration versus peak area is that this assay is from 5 to 500 mM with a detection limit of 0.1-0.2 mM. 

In capillary zone electrophoresis microchips, where the background electrolyte consists only of aqueous buffer, analytes are separated based on a size-to-charge ratio, and neutral analytes are not resolved from each other. 

Eberle et al. [134] separated the enantiomers of omeprazole and structurally related drugs by capillary zone electrophoresis with bovine serum albumin as chiral selector. The separations were carried out on a fused silica column (60 cm x 50 pm, 50 cm to detector) with a buffer consisting of 100-/zM-bovine serum albumin and 7% 1-propanol in 10 mM potassium phosphate pH 7.4. Electrokinetic injection was at 5-8 kV for 7 s. An applied voltage of 300 V/cm was used. Detection was at 290 nm. Detection limits were 0.04 mg/ml for the analytes studied. 

Lin and Wu [137] established a simple capillary zone electrophoresis method for the simultaneous analysis of omeprazole and lansoprazole. Untreated fused-silica capillary was operated using a phosphate buffer (50 mM, pH 9) under 20 kV and detection at 200 nm. Baseline separation was attained within 6 min. In the method validation, calibration curves were linear over a concentration range of 5-100 /iM, with correlation coefficients 0.9990. RSD and relative error were all less than 5% for the intra- and interday analysis, and all recoveries were greater than 95%. The limits of detection for omeprazole and lansoprazole were 2 fiM (S/N = 3, hydroxynamic injection 5 s). The method was applied to determine the quality of commercial capsules. Assay result fell within 94—106%. 

Berzas Nevado et al. [138] developed a new capillary zone electrophoresis method for the separation of omeprazole enantiomers. Methyl-/ -cyclodextrin was chosen as the chiral selector, and several parameters, such as cyclodextrin structure and concentration, buffer concentration, pH, and capillary temperature were investigated to optimize separation and run times. Analysis time, shorter than 8 min was found using a background electrolyte solution consisting of 40 mM phosphate buffer adjusted to pH 2.2, 30 mM /1-cyclodextrin and 5 mM sodium disulfide, hydrodynamic injection, and 15 kV separation voltage. Detection limits were evaluated on the basis of baseline noise and were established 0.31 mg/1 for the omeprazole enantiomers. The method was applied to pharmaceutical preparations with recoveries between 84% and 104% of the labeled contents. 

Capillary Zone Electrophoresis. The primary advantage of capillary electrophoresis can be found in the simplicity of the instrument. Basic experimental components include a high-voltage power supply, two buffer reservoirs, a fused silica capillary, and a detector. The basic setup is usually completed with enhanced features such as multiple injection devices, autosamplers, sample and capillary temperature controls, programmable power supplies, multiple detectors, fraction collection, and computer interfacing. 

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