Spectrophotometric determination of antiallergic drug in bulk powder and in its pharmaceutical formulations

Two simple, rapid and selective spectrophotometric methods have been described for the determination of promethazine hydrochloride (PMH) either in pure or pharmaceutical formulations. The methods are based on the formation of a green colored product with sulphanilic acid (SPA) in presence of N-bromosuccinimide (NBS) or a red colored, chloroform soluble product with p-nitroaniline (PNA) in presence of ceric ammonium sulphate (CAS). The chromogen formed has maximum absorption at 600 nm and at 510 nm with SPA and PNA, respectively. The optimum reaction conditions and other analytical parameters are evaluated. Beer's law is valid in the concentration range of 0.5-25 mug/mL (R = 0.9983) with SPA and 2-75 mug/mL (R = 0.9981) with PNA. Molar absorptivity values as calculated from the Beer's law data are 5.54 x 10(3) L/mol/cm and 3.05 x 10(3) L/mol/cm for SPA and PNA, respectively. The results are in good agreement with those of the official method. No interference was observed from common pharmaceutical excipients.