Capillary zone electrophoresis of basic drugs in non-aqueous acetonitrile with buffers based on a conventional pH scale

The pK(a)(*) valves of 10 nitrogen-containing basic drugs in non-aqueous ac etonitrile were determined from the pH* dependence of their electrophoretic mobilities. The pH* scale in the organic solvent was established using bac kground electrolytes with known conventional pK(a)(*) values, making furthe r calibration with reference pH electrodes unnecessary. In acetonitrile the pK(a)(*) valves of analytes (or their conjugated cation acids, BH+, respec tively) were 5.2 - 8.9 pK units > those in water. The observed change in pK (a)(*) values of cationic analytes was, however, much less than the known r espective change for neutral acids type HA. From the pK(a)(*) values and th e actual mobilities, it is possible to predict pH* conditions to enable sep aration of analytes, and this was demonstrated for two pairs of common drug s.