3-Aminobenzamide and 3-aminobenzoic acid, tags for capillary electrophoresis of complex carbohydrates with laser-induced fluorescent detection

The efficiencies in derivatization of reducing carbohydrates were compared by capillary electrophoresis using maltose as a model with nine monoaminobenzene derivatives by reductive amination in the presence of sodium cyanoborohydride. We found that aminobenzene derivatives substituted at the 3-position showed good reactivity with reducing carbohydrates as expected from the reaction mechanism, although the fluorescence intensities and molar absorptivities of these derivatives were not as high as those of 2- and 4-aminobenzene derivatives. The reagents, 3-aminobenzamide and 3-aminobenzoic acid, which showed the highest reactivity, were applied to the labeling of carbohydrate chains obtained from some sialic acid-containing glycoprotein samples, and also high-mannose and hybrid-type oligosaccharides. Capillary electrophoresis of these labeled carbohydrate chains in an inner surface-modified capillary with (50% phenyl)methylpolysiloxane allowed excellent separation of sialic acid-containing carbohydrate chains derived from fetuin and thyroglobulin as well as high mannose-type and hybrid-type carbohydrates derived from bovine pancreas ribonuclease B, soybean agglutinin and hen ovalbumin. The lower limit of calibration was as low as the 10(-16) mol (injected amount) with helium-cadmium laser induced detection.