Affinity Capillary Electrophoresis of Oligosaccharides

The basic separation mode of capillary electrophoresis is zone electrophoresis (ZE). In this mode solutes having different charge-to-size ratios migrate through an electrophoretic solution with different velocities, forming separate zones. ZE is a simple mode performable in an electrophoretic solution composed of a common salt, such as sodium acetate, sodium phosphate, and so forth, but is not applicable to nonionic compounds. Because most carbohydrates are electrically neutral under normal conditions, such analytes must be changed to ions prior to or during analytical runs. A number of methods have been developed for the precapillary conversion to cationic (e.g., see refs. 1–4) or anionic (e.g., 5–8) derivatives based on reductive amination. The derivatives of the former type are positively charged in acidic media as a result of the introduction of the imino group. The derivatives of the latter type have either the carboxyl group or the sulfonate group in addition to the imino group. They give cations or anions dependent on the pH of the electrophoretic solution. The derivatives having the sulfonate group, which is strongly dissociated, behave as high-mobility anions in neutral or alkaline media.