Spectrophotometric promethazine hydrochloride determination using bromcresol green.

A spectrophotometric method was developed for determining promethazine hydrochloride (I) complexed with bromcresol green and then extracted with chloroform. The complex in chloroform showed maximum absorption at 415 nm and obeyed Beer's law over 1.2-8.5 micrograms/ml. The complex molar absorptivity was 1.93 X 10(4) M. Complex formation and extraction were complete and quantitative over pH 2.7-2.8. The promethazine hydrochloride-bromcresol green molar ratio was 1:1. Excipients, coloring matter, flavoring agents, and other substances likely to be present in promethazine preparations did not interfere in the determination. Direct determination in tablet, syrup, and injection preparations were carried out satisfactorily.