Medium-throughput pKa screening of pharmaceuticals by pressure-assisted capillary electrophoresis

A fast screening method for the determination of the dissociation constants (pK(a)) of acidic, basic, and multivalent compounds was developed by using pressure-assisted capillary electrophoresis (PACE). External air pressure was applied to shorten the analysis time. The separation efficiency decreas es as air pressure increases. However, it was found that air pressure does not affect the measurement of electrophoretic mobility and pK(a) significan tly when it is less than 2 psi. The method was evaluated in terms of accura cy, precision, and ruggedness by using a set of 48 compounds with literatur e pK(a) values ranging from 2 to 10. The difference between the measured pK (a) values and literature values is less than 0.2 units. The throughput is approximately 20 compounds per day with a 12-point measurement ranging from pH 2.5 to 11. It was demonstrated that this method is applicable for pK(a) screening of pharmaceuticals with diverse chemical structures.