Determination of Binary Mixtures of Levodopa and Benserazide in Pharmaceuticals by Ratio-Spectra Derivative Spectrophotometry

Binary mixtures of l-dopa (LD) and benserazide (BEN) are analyzed by ratio spectra first derivative spectrophotometry. The procedures are accurate, non-destructive and do not require any separation step. This method depends on first derivative of the ratio spectra by division of the absorption spectrum of the binary mixture by a standard spectrum of one of the components and then calculating the first derivative of the ratio spectrum. The first derivative of the ratio amplitudes at 287.7 nm for LD and 251.4 nm for BEN was selected for the determination. Beer's law was obeyed in a range of concentration from 10 to 70 µg/ml for LD and from 5 to 50 µg/ml for BEN. The method was successfully applied for determining of two drugs in synthetic mixtures and in pharmaceutical preparations.