INVESTIGATION OF EXPERIMENTAL APPROACHES TO THE DETERMINATION OF PK(A) VALUES BY CAPILLARY ELECTROPHORESIS

The calculation of pk(a) values from capillary electrophoresis data may be accomplished in several ways. Electrophoretic mobilities are fitted to a model which describes the dissociation versus the pH. For a linear model, a linear regression approach yields biased results. Weighted linear regression requires many replicates to determine weighting factors and is thus a time-consuming experiment. For an exponential model, non-linear regression of the electrophoretic mobilities in different, equally pH spaced buffers of the analyte gives the least biased determination. Another experimental approach to this determination is to use a permanently charged solute to correct for potential biases in the expected electrophoretic mobilities obtained between different buffers. In the buffer series chosen, there was no significant bias observed. Buffer pH may be determined by an in situ approach using an internal standard of known pK(a). However, the precision obtained is much less than using a pH meter.