Capillary electrophoresis of carboxylated carbohydrates III. Selective precolumn derivatization of glycosaminoglycan disaccharides with 7- aminonaphthalene-1,3-disulfonic acid fluorescing tag for ultrasensitive laser-induced fluorescence detection

Eight different glycosaminoglycan-derived disaccharities were selectively labeled via their carboxylic acid group with 7-aminonaphthalene- 1,3-disulfonic acid (ANDSA) by a condensation reaction between the amino group of ANDSA and the carboxylic acid group of the saccharides in the presence of water-soluble carbodiimide. This derivatization reaction yielded stable derivatives with percentage yields as high as 97%. The ANDSA disaccharide derivatives were readily detected by on-column laser induced fluorescence (LIF) with a He-Cd laser at 325 nm. With LIF, the limit of detection was at the nanomolar level, three orders of magnitude lower than the limit of detection of underivatized disaccharides in the uv at 231 nm. In addition, due to the presence of two strong sulfonic acid groups in the ANDSA tag, the derivatives were readily separated at acidic pH (i.e., pH 4.0-5.0) using 100 mM sodium acetate buffers as the running electrolytes. The addition of polycationic spermine in small amounts to the running electrolytes provided different selectivity with baseline resolution in the pH range 6.0- 7.0, and the excess ANDSA migrated ahead of the ANDSA disaccharides.