AN05 Measurement of extreme pKas

The determination of pKas outside of the range 3 – 11 using potentiometric methods can prove problematic, due to the high buffer capacity of water and the relatively poor performance of pH electrodes at the extremes of the pH range. Capillary electrophoresis methods also perform poorly in this range. It is also true that predicted pKa values are less reliable at the extremes of the pKa range. This application note describes some experimental designs for the SiriusT3 which may be used to overcome these problems, giving reliable pKa values between 0.7 and >13.