A fast high throughput method for the determination of acidity constants by capillary electrophoresis. 3. Basic internal standards

A set of 25 monoprotic bases is proposed as internal standards for pKa determination by capillary electrophoresis. The pKa of the bases is determined and compared with available literature data. The capillary electrophoresis internal standard method offers numerous advantages over other typical methods for pKa determination, especially of analysis time and buffer preparation. However, it requires disposing of appropriate standards with reference pKa value. The set of bases established in this work together with the set of acids previously established provide a reference set of compounds with well-determined acidity constants that facilitate the process of selecting appropriate internal standards for fast pKa determination by capillary electrophoresis in high throughput screening of pharmaceutical drugs. In addition, the performance of the method when acidic internal standards are used for the determination of acidity constants of basic internal standards has also been tested. Although higher errors may be expected in this case, good agreement is observed between determined and literature values. These results indicate that in most cases structural similarity between the analyte and the internal standard might not be an essential requirement in the internal standard method.