Kinetic-spectrophotometric determination of propylthiouracil based on its inhibitory effect on the reduction of neutral red by hypophosphite

A new kinetic-spectrophotometric method for determination of propylthiouracil (PTU) is described. The proposed method is simple, rapid, inexpensive and sensitive for the determination of PTU in pure and tablet forms. This method is based on the inhibitory effect of propylthiouracil on the palladium(II)-catalyzed reaction between neutral red and hypophosphite ions. The effect of various parameters such as: dye, hypophosphite, and Pd(II) concentrations, pH, ionic strength, and temperature were optimized. Two distinct linear calibration graphs were observed in the ranges 0.006–0.033 (n = 6, r = 0.9991) and 0.033–0.300 ppm (n = 10, r = 0.9980). The variable time method was used. The limit of detection was 0.004 ppm. The proposed method was applied for the determination of propylthiouracil in pure and tablet forms.