Chromatographic Determination of Dissociation Constants of Pramipexole and its Impurities

The main goal in this investigation was monocratic HPLC determination of dissociation constant values (pK _a) of pramipexole and its impurities, BI-II 546 CL, BI-II 751 xx and 2-aminobenzothiazole. The chromatographic method is advantageous as a small amount of substance is needed and the degree of substance purity is less important. Analysis was carried out using stationary phases stable in a wide pH range. Triethylamonium phosphoric buffer was selected as appropriate pH controlling solution because it can cover a wide pH range. Detection was done on two different wavelengths, 262 nm for pramipexole, BI-II 751 xx and 2-aminobenzothiazole and at 326 nm for BI-II 546 CL. The constants were calculated from the typical sigmoidal curves of analyte obtained as retention factor versus the pH of the mobile phase.