Spectrophotometric determination of certain vicinal dihydroxybenzene derivatives with sodium bismuthate

A simple and accurate spectrophotometric method is developed for the determ ination of certain vicinal. dihydroxybenzene derivatives, namely, dopamine (DPH), levodopa (LD), methyldopa (MD) and pyrocatechol (PC) using sodium bi smuthate in an acid medium. The method is based on the formation of a yello w colored product by the oxidation of vicinal dihydroxybenzene derivatives using sodium bismuthate. Beer's law was obeyed over the concentration range of 8-130 mug/ML with the maximum absorption at 422-429 nm. The molar absor ptivity and Sandell's sensitivity as evaluated from Beer's law data were fo und to be in the range of 1.02-1.34 X 10(-3) L mol(-1) cm(-2) and 108-185 n g/cm(2) respectively. The proposed method has been successfully applied for the determination of DPH, LD and MD in injections and tablets of pharmaceu tical preparations. The reliability of the methods was established by repli cate determinations with the reported and official method.