HIGH-EFFICIENCY CAPILLARY ELECTROPHORETIC SEPARATION OF BASIC-PROTEINS USING COATED CAPILLARIES AND CATIONIC BUFFER ADDITIVES - EVALUATION OF PROTEIN CAPILLARY WALL INTERACTIONS

The joint use of basic cationic additives (morpholine and several tetraazamacrocycles) in the buffer and chemically bonded cross-linked polyacrylamide-coated capillaries was evaluated as a method for decreasing the adsorption of basic proteins on the fused-silica capillary wall. The superiority of the tetraazamacrocycle Cyclen (1,4,7,10-tetraazacyclododecane) over morpholine and other tetraazamacrocycles is demonstrated. Using 20 mM phosphate-60 mM Cyclen buffer (pH 5.5) and cross-linked polyacrylamide-coated capillaries, separation efficiencies in the range of 10(6) plates/m were obtained for basic proteins. A simplified model that allows the quantification of the interactions between proteins and the capillary wall was developed. The model was assessed using the different buffers and capillaries evaluated in the first part. As the model predicts, a straight line for the plot of the inverse of the migration time versus the electric field strength with an intercept different from zero was observed. The value of the intercept correlates with the separation efficiency observed for the basic proteins studied and, therefore, with the interaction strength between proteins and the capillary wall.