AUTOMATED PK(A) DETERMINATION AT LOW SOLUTE CONCENTRATIONS BY CAPILLARY ELECTROPHORESIS

Capillary electrophoresis is investigated for the determination of thermodynamic pK(a) measurements at low solute concentrations, a current limitation of potentiometric titrations. It is not necessary to accurately know the concentration of a titrant or solute. The method relies on measuring the ionic mobility of the solute as a function of pH. Mobility and pH data are fitted to an equilibrium expression with a non-linear regression. The detection limit for benzoic acid is 2 mu M. Equations are introduced to remove the need to measure buffer pH outside of the capillary and to handle potential discontinuities in solute mobility between different buffer solutions caused by changes in the shape of the solute molecule and the buffer viscosity.