Capillary electrophoresis running buffer, additives

P Sun, N Wu, GE Barker, RA Hartwick. Chiral separations using dextran and bovine serum albumin as run buffer additives in affinity capillary electrophoresis. J Chromatogr 648 475-480, 1993. 

KH Ekborg-Ott, GA Zientara, JM Schneiderheinze, K Gahm, DW Armstrong. Avo-parcin, a new macrocyclic chiral run buffer additive for capillary electrophoresis. Electrophoresis 20 2438-2457, 1999. 

Imidazolium ILs easily form micro-emulsions using different surfactants such as long-chain alcohols and the properties of the new micelle-ionic liquid soluhons can be explored in inverse gas chromatography processes [124]. Moreover, ILs have been used as run buffer additives in capillary electrophoresis [125] and as ultra-low-volatility liquid matrixes for matrix-assisted laser desorption/ionizahon mass spectrometry [126]. 

Micellar electrokinetic chromatography uses ionic surfactants at a concentration above the critical micelle concentration (CMC) as a component of the run buffer chosen to separate compounds. This generates a pseudo-stationary phase that performs the separation. This technique is therefore optimal for separating neutral and charged compounds from each other. In addition compounds that are very hydrophobic, and those typically insoluble in traditional capillary electrophoresis run separate buffers under these conditions. Neutral compounds elute in the order of their hydrophobicity. 

Lin et al. [95] used capillary electrophoresis with dual cyclodextrin systems for the enantiomer separation of miconazole. A cyclodextrin-modified micellar capillary electrophoretic method was developed using mixture of /i-cyclodextrins and mono-3-0-phenylcarbamoyl-/j-cyclodextrin as chiral additives for the chiral separation of miconazole with the dual cyclodextrins systems. The enantiomers were resolved using a running buffer of 50 mmol/L borate pH 9.5 containing 15 mmol/L jS-cyclodextrin and 15 mmol/L mono-3-<9-phcnylcarbamoyl-/j-cyclodextrin containing 50 mmol/L sodium dodecyl sulfate and 1 mol/L urea. A study of the respective influence of the /i-cyclodcxtrin and the mono-3-(9-phenylcarbamoyl-/i-cyclodextrin concentration was performed to determine the optical conditions with respect to the resolution. Good repeatability of the method was obtained. 

Chiral crown ethers can be generally utilized as chiral selectors. They have been used as additives to mobile phases or running buffer in MECK and capillary electrophoresis (CE) systems124,125 (see Section 3.1.6.4.). 

Capillary electrophoresis (CE) provides a valid alternative to HPLC methods for chiral separations. The direct resolution of racemates requires only an enantiomerically pure additive (chiral selector) to be dissolved in the running buffer. The experimental conditions affecting the separations and an overview of practical applications have been compiled <1999ELP2605>. 

Capillary electrophoresis has become extremely important in several application areas (a) enantiomeric separations can be achieved by the simple addition of a chiral additive to the run buffer (b) rapid and distinctive profiles for different isoform groups can be obtained by reversed-charge CE separations of heterogeneous mixtures and (c) inorganic and organic ion determination has improved significantly with new detection systems. 

There are numerous modes of operation in CE. Capillary zone electrophoresis (CZE) is the simplest mode and it was chosen by many authors for PSP toxin analysis. CZE is based on the different migration of solutes in an electric field and toxin separation is performed in narrow-capillaries, which are usually filled only with buffer. Separation occurs because PSP toxins migrate in discrete zones and at different velocities. In this EC mode, selectivity can be readily altered through changes in running buffer pH or by the use of buffer additives. 

Nieto, O., Hernandez, R, and Hernandez, L., Capillary zone electrophoresis of human recombinant erythropoietin using Cg coated columns without additives in the running buffer. Anal. Commun., 33, 425, 1996. 

Capillary electrophoresis is primarily limited to small molecules that are water solul le because of their compatibility with the run buffer. Other similar techniques such as isoelectric focusing and capillary zone elec-trophoresis ° have aided in the separation of proteins by allowing for the separation of larger proteins. In addition these techniques can separate isoforms of proteins and peptides by using an extraordinarily low pH range. However, capillary electrophoresis cannot separate neutral compounds, and... 

Ren et al. [109] established a method for the simultaneous determination of anisodamine, scopolamine, atropine, and anisodine by capillary electrophoresis with electrochemiluminescence detection (CE-ECL). The concentration and pH of the running buffer as well as the methanol content additive were investigated for the improvement of selectivity and sensitivity. These four alkaloids were separated within 6 min under optimal conditions in a buffer containing 20 mmol L phosphate and 7 % methanol at pH 8.0. The method, showing RSD of the migration time less than 1.1 % and recoveries between 97.8 % and 102 %, was applied for the determination of anisodamine and scopolamine in an extract of Przewalskia tangutica. 

Cheung, H.Y, Zhang, Q.R Enhanced analysis of1riterpenes,flavonoids and phenohc compounds in f rtt c//avM/garis L. hy capillary zone electrophoresis with die addition of running buffer modifiers. J. Chromatogr. A. 1213(2), 231-238 (2008)... 

Separation by electrophoresis is based on differences in analyte velocity in an applied electric field within the capillary. The electrophoretic mobility of the analyte (ji ) depends on the characteristics of the analyte (electrical charge, molecular size, and shape) and the characteristics of the running buffer (type and ionic strength of the electrolyte, pH, viscosity, and properties of the additives) in which the migration takes place [1-3]. 

For classical electrophoresis, samples of 0.1-1 cm are loaded into wells formed in gel slabs or layered onto the tops of gel columns, often with the addition of a sucrose solution to increase the density. For CE and CEC, much smaller samples (1-50 nl) are drawn into one end of the capillary (usually the anodic end) from a sample vial, either hydrod3mamically using gravity, positive pressure or a vacuum, or electrokinetically by applying a voltage for a short time when the EOF causes the sample components to migrate into the capillary. The reproducibility of sample injection into capillaries, typically 0.5-3%, is variable, and electrokinetic methods may discriminate between components of a mixture because of differences in electrophoretic mobilities. Time, temperature, pressure drops and sample and running buffer viscosities are all sources of variability, and automated sample injection is preferable to minimize these effects. 

Modes of electrophoresis are defined by the nature and form of the supporting medium, the running buffer and any incorporated additives. For capillary electrochromatography (CEC), the capillary is filled with a stationary phase similar to those used in HPLC. 

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