Simultaneous spectrophotometric determination of drotaverine hydrochloride and paracetamol in tablet

Two simple, accurate and reproducible spectrophotometric methods; Q analysis and first order derivative method have been described for the simultaneous estimation of drotaverine hydrochloride and paracetamol in combined tablet dosage form. Absorption maxima of drotaverine hydrochloride and paracetamol in distilled water were found to be 303.5 nm and 243.5 nm respectively. Beer's law was obeyed in the concentration range 5-50 mug/ml for drotaverine and 5-60 mug/ml for paracetamol. In Q analysis method, two wavelengths were selected at isobestic point (277 nm) and lambda(max) of paracetamol (243.5 nm). In first order derivative method, zero crossing point for drotaverine hydrochloride and paracetamol were selected at 303.5 nm and 243.5 nm, respectively. The results of two methods were validated statistically and recovery studies were found to be satisfactory.