Background electrolyte capillary electrophoresis separation

The synthesis of a new CIL [S-(—)-2-hydroxymethyl-l,l-dimethylpyrrolidinium tetrafluoroborate] derived from L-proline alcohol have been reported by Maier et al. [78]. This CIL was found to be an effective additive to acidic background electrolytes affording the separation of a mixture of five tricyclic antidepressants using capillary zone electrophoresis (CZE). The addition of the CIL to acidic background electrolytes leads to suppression of the magnitude of electroosmotic flow (EOF) and gradually reversed the direction of the EOF. Baseline separation of the five model analytes was achieved. It was observed that the proline-derived CIL offers relatively smaller anodic EOF compared to cationic surfactants that are mostly used for... 

Enantioresolution in capillary electrophoresis (CE) is typically achieved with the help of chiral additives dissolved in the background electrolyte. A number of low as well as high molecular weight compounds such as proteins, antibiotics, crown ethers, and cyclodextrins have already been tested and optimized. Since the mechanism of retention and resolution remains ambiguous, the selection of an additive best suited for the specific separation relies on the one-at-a-time testing of each individual compound, a tedious process at best. Obviously, the use of a mixed library of chiral additives combined with an efficient deconvolution strategy has the potential to accelerate this selection. 

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. ... 

Figure 26-31 Separation of natural isotopes of 0.56 mM Cl by capillary electrophoresis with indirect spectrophotometrlc detection at 254 nm. Background electrolyte contains 5 mM CrOJ to provide absorbance at 254 nm and 2 mM borate buffer, pH 9.2. The capillary had a diameter of 75 m, a total length of 47 cm (length to detector = 40 cm), and an applied voltage of 20 kV. The difference in electrophoretic mobility of 36C and 37CI is just 0.12%. Conditions were adjusted so that electroosmotlc flow was nearly equal to and opposite electrophoretic flow. The resulting near-zero net velocity gave the two isotopes maximum time to be separated by their slightly different mobilties. [From C. A Lucy and T. L McDonald, "Separation of Chloride Isotopes by Capillary 35 40 45 Electrophoresis Based on the Isotope Effect on Ion Mobility"Anal.

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. 

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 affinity electrophoresis (CAE) or affinity capillary electrophoresis (ACE) — An electrophoretic separation technique (- electrophoresis), in which -> analytes are separated in a capillary, with the -> supporting (background) electrolyte containing substances capable of specific, often biospecific, interactions with the analytes. Ref [i] Riekkola ML, Jonsson jA, Smith RM (2004) Pure Appl Chem 76 443... 

Capillary sieving electrophoresis (CSE) — An electrophoresis technique, in which analytes are separated in a capillary, containing a sieving medium (e.g., an entangled polymer network) in the -> supporting (background) electrolyte. The separation is based on differences in size and shape of the charged analytes. 

The solution contained within the capillary in which the separation occurs is known as the background electrolyte (BGE), carrier electrolyte, or, simply, the buffer. The BGE always contains a buffer because pH control is the most important parameter in electrophoresis. The pH may affect the charge and thus the mobility of an ionizable solute. The electro-osmotic flow (EOF) is also affected by the buffer pH. Table 1 contains a list of buffers that may prove useful in high-performance capillary electrophoresis (HPCE). As will be seen later, only a few of these buffers are necessary for most separations. 

The increased need for stereoselective analyses has induced a tremendous development of analytical techniques resolving enantiomers. Among these techniques, liquid chromatography, and more recently capillary electrophoresis (CE), are recognized as methods of choice for the chiral separation of pharmaceutical compounds. Chiral discrimination by CE is generally achieved with the direct separation method where the chiral selector is simply added to the background electrolyte (BGE). 

Most CE work so far has been done using the capillary zone electrophoresis (CZE) mode, where analytes are separated on the basis of differences in electrophoretic mobility, which is related to charge density. The separation is carried out in a capillary filled with a continuous background electrolyte (buffer). Micellar electrokinetic capillary chromatography (MEKC or MECC) is one other CE method based on differences in the interaction of the analytes with micelles present in the separation buffer, which can easily separate both charged and neutral solutes with either hydrophobic or hydrophilic properties. An alternative to MEKC is capillary... 

Fillet M., Servais A.C., Crommen J., Effects of background electrolyte composition and addition of selectors on separation selectivity in nonaqueous capillary electrophoresis. Electrophoresis, 24, 1499-1507 (2003). 

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