High-performance capillary electrophoretic separation of carbohydrates with indirect UV detection using diethylamine and borate as electrolyte additives.

The separation of underivatized carbohydrates was investigated using capillary zone electrophoresis with indirect UV detection based on sorbic acid or riboflavin. In comparison with sodium hydroxide, the separation of carbohydrates was greatly improved using diethylamine (DEA) as an electrolyte additive. Since the conductivity of DEA is much lower than that of sodium hydroxide, a stable baseline and a 3-5 times improvement in separation efficiency was observed at a pH as high as 12.6. It was found that DEA reduced the electrophoretic mobility of carbohydrates by formation of ion-pairs, and also reduced the electroosmotic flow by masking the silanol groups at the capillary surface. Many monosaccharides, including glucose, rhamnose, mannose, and fructose, which have very similar pKa values, were completely separated using 5% DEA at pH 12.6. The separation of di- and trisaccharides using indirect detection with a borate buffer at pH 9.5 was also investigated. The separation of disaccharides was greatly improved with borate complexation using riboflavin as a background electrolyte (BGE) over the sodium hydroxide and DEA electrolyte system with sorbic acid as BGE. The resolution of carbohydrates increased as pH increased, and sucrose, trehalose, raffinose, and maltotriose were successfully separated at pH 11.8.