Factors that influence separation capillary electrophoresis

Anions and uncharged analytes tend to spend more time in the buffered solution and as a result their movement relates to this. While these are useful generalizations, various factors contribute to the migration order of the analytes. These include the anionic or cationic nature of the surfactant, the influence of electroendosmosis, the properties of the buffer, the contributions of electrostatic versus hydrophobic interactions and the electrophoretic mobility of the native analyte. In addition, organic modifiers, e.g. methanol, acetonitrile and tetrahydrofuran are used to enhance separations and these increase the affinity of the more hydrophobic analytes for the liquid rather than the micellar phase. The effect of chirality of the analyte on its interaction with the micelles is utilized to separate enantiomers that either are already present in a sample or have been chemically produced. Such pre-capillary derivatization has been used to produce chiral amino acids for capillary electrophoresis. An alternative approach to chiral separations is the incorporation of additives such as cyclodextrins in the buffer solution. 

Free-solution capillary electrophoresis (FSCE) is the major technique used for drug analysis, considering the fact that many drugs have acidic or basic groups that allow them to analyzed as charged molecules. In this technique, the capillary is filled with a buffer solution and the separation is based on the different electrophoretic mobilities of the solutes. Separation of both anionic and cationic solutes is possible, owing to electro-osmotic flow (EOF). The pH of the buffer has a major influence on selectivity, but other factors such as buffer concentration, additives, etc. should also be considered dining method development. ... 

In 1996, the capillary zone electrophoresis (CZE) separation of a model mixture of six anthocyanins was reported using a 150-mM borate buffer at pH 8 (Bridle et al., 1996). It was proposed that the separation was influenced by three factors electro-osmotic flow (EOF), charge/mass ratio, and complex formation with borate. Bridle and Garcia-Viguera (1997) compared HPLC and CZE for the separation of strawberry and elderberry anthocyanins. They used fused-silica capillaries (57 cm X 75 fim i.d.), mn at 25°C with 150 mM sodium borate buffer (pH 8.0). A more concentrated sample (87 times) was needed for equivalent CZE response at pH 8 compared to HPLC at pH 1.8 because of the much smaller sample introduction volume, the shorter detector ceU path length, and the smaller proportion of colored anthocyanin species at pH 8.0. The separation of strawberry anthocyanins by CZE was satisfactory but the separation of elderberry anthocyanins by CZE was marred by the presence of a large baseline hump. The baseline rise may have been caused by interfering compounds in the extract (i.e., colored polymers) which did not affect the... 

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