DETERMINATION OF THE ISOELECTRIC POINTS OF LOW AND HIGH-MOLECULAR-MASS AMPHOLYTES BY CAPILLARY ELECTROPHORESIS

A methodology for a reliable and absolute determination of isoelectric points of amphoteric species by capillary zone electrophoresis is pro posed. The principle of this absolute method consists in the applicati on of an additional electroosmotic and/or hydrodynamic flow of a backg round electrolyte. This allows the measurement of electrophoretic mobi lities of substances close to their isoelectric points where the net e lectric charge is very low and electrophoretic mobility tends to zero. The mobilities are measured at various pH values of the electrolyte s o as to find the pH at which the substance moves through the separatio n column at zero mobility under the action of the additional flow only . The number of required measurements is lowered to the minimum with t he help of the iterative procedure based on the Regula Falsi algorithm . The precision of the proposed method is predicted theoretically. The feasibility is demonstrated on real samples. The isoelectric points o f histidine, myoglobine and ribonuclease are found from their titratio n curves.