Determination of pKa values of organic bases in aqueous acetonitrile solutions using capillary electrophoresis

Capillary electrophoresis (CE) was used for the determination of ionisation constants (pK(a)) of a variety of organic bases in aqueous acetonitrile solutions over the range 0-60% (vW/v) acetonitrile. These bases are used as test compounds in HPLC column evaluation, thus knowledge of their pK(a) in hydro-organic solutions is useful. The base pK(a) decreased with acetonitrile concentration and significant shifts from the aqueous pK(a) (up to -0.8) were found using 60% acetonitrile. The CE application was confirmed to be very suitable for fast and accurate pK(a) measurement in aqueous organic solutions. (C) 2003 Elsevier B.V. All rights reserved.