Capillary electrophoretic studies of acid–base properties of sanguinarine and chelerythrine alkaloids

Capillary zone electrophoresis with UV detection was used for determination of dissociation constants of alkaloids sanguinarine and chelerythrine. Despite the limited solubility of the uncharged forms of the alkaloids resulting in insufficient analytical signal at higher pH the reliable dissociation constants were obtained when acidified samples containing low amount of the alkaloid were injected into the capillary. The precipitation of the alkaloid in the capillary induced by injecting sample of low pH into the background electrolyte of higher pH does not affect the mobility of the alkaloid if its concentration injected exceeds the solubility only to a small extent. Dissociation constants (pKR+) of sanguinarine and chelerythrine calculated to 8.3 ± 0.1 and 9.2 ± 0.1, respectively, are relevant to Good buffers of ionic strength of 30 mM.