SIMULTANEOUS DETERMINATION OF NITROFURANTOIN AND PHENAZOPYRIDINE IN PHARMACEUTICAL PRODUCTS BY DERIVATIVE SPECTROPHOTOMETRY AND BY THE DERIVATIVE OF THE RATIO SPECTRA

Two methods are described for determining nitrofurantoin and phenazopyridine in mixtures by first and second derivative spectrophotometry. The procedures do not require any separation step. Measurements were obtained at the zero-crossing wavelengths by both methods. Calibration graphs were found to be linear up to 33 mug/ml (nitrofurantoin) and to 18 mug/ml (phenazopyridine). Nitrofurantoin in the presence of phenazopyridine was also determined by the first derivative of the ratio spectra. The methods were applied to determine the two compounds in a pharmaceutical product.