Spectrophotometric Determination of Tiopronin in Pharmaceutical Samples by Phosphorus Molybdenum Blue

A no vel method is established for spectrophotometric determination of tiopronin by phosphorus molybdenum blue. It is based on the fact that PO43- reacts with MoO246 in 0.47 mol/L H2SO4 solution to form a product of phosphorus molybdenum heteropoly acid ([H2PMo12O40](-)) which is reduced to phosphorus molybdenum blue (H3PO4 center dot 10MoO(3)center dot Mo2O5) by tiopronin. The absorbance of phosphorus molybdenum blue is measured at the absorption maximum of 730 nm and the amount of tiopronin can be determined based on this absorbance. Absorbance is linear with the concentration of tiopronin in the range of 16-40 mu g/mL and the regression equation is A = -0.1193 + 0.01927c (mu g/mL) with a correlation coefficient of 0.9989 and the apparent molar absorption coefficient of 3.14 x 10(3) L/(mol cm). The detection limit and the RSD are 1 mu g/mL and 0.92%, respectively. Thus, the method is validated and commonly available to determine tiopronin in pharmaceutical samples.