Improved capillary zone electrophoretic separation of basic proteins in uncoated fused-silica capillary by using ethylene diamine as a buffer additive

Abstract

Ethylene diamine was used as a buffer additive to improve capillary zone electrophoretic separation of basic proteins in an uncoated fused-silica capillary and theoretical plate numbers of the order of a hundred thousand were obtained for all five standard proteins at pH 6.5, 8.0 and 9.5. The critical factors that affected the separation efficiency were the ethylene diamine concentration and the applied voltage at each pH value. Adsorption of ethylene diamine ions to the capillary inner wall significantly reduced the charge density of the wall, and therefore reduced the adsorption of basic proteins. Increasing the concentration of ethylene diamine increased this reduction, and caused an increase in the theoretical plate numbers of all proteins. Increasing the applied voltage caused an increase in the theoretical plate numbers of all proteins in the low-voltage region and a decrease in high-voltage region, which maybe attributed to excessive Joule heat.