Chemistry of nonaqueous titration of chlopromazine

The chemistry of the red color formed during perchloric acid titration of chlorpromazine hydrochloride in acetic acid in the presence of mercuric acetate is discussed. Addition of ascorbic acid prevents the color formation and allows titration using a crystal violet end-point. Ascorbic acid addition also sharpens the potentiometric end-point. Ascrobic acid and its oxidation product, dehydroascorbic acid, being neutral to perchloric acid, do not interfere with the titration.