Spectrophotometric determination of catecholamine using vanadium and eriochrome cyanine r

A highly sensitive spectrophotometric method for the analysis of catecholamine drugs; L-dopa and methyldopa, is described. The analysis is based on the reaction of drug molecules with vanadium (V) which is reduced to vanadium (IV) and form complex with eriochrome cyanine R to give products having maximum absorbance (lmax) at 565 nm. Beer's law is obeyed in the range 0.028-0.84 and 0.099-0.996 mg mL-1 for L-dopa and methyldopa, respectively. The statistical analysis as well as comparison with reported methods demonstrated high precision and accuracy of the proposed method. The method was successfully applied in the analysis of pharmaceutical preparations.