Determination of thiamazole in pharmaceutical samples by phosphorus molybdenum blue spectrophotometry

A novel method is established to determine thiamazole by phosphorus molybdenum blue spectrophotometry. The experiment indicates that PO43- reacts with Mo7O246- in 0.30 mol/LH2SO4 solution to form a product with phosphorus-molybdenum heteropoly acid ([H2PMo12O40](-)). Then [H2PMo12O40](-) is deoxidized to form phosphorus molybdenum blue (H3PO4 center dot 10MoO(3)center dot Mo2O5) by thiamazole. The amount of thiamazole can be determined based on the absorbance of phosphorus molybdenum blue (lambda(max) = 710 nm). A good linear relationship is obtained between the absorbance and the concentration of thiamazole in the range of 0.035-70 mu g/mL. The equation of the linear regression is A=0.03384 + 0.00834c (mu g/mL), with a linear correlation coefficient of 0.9990. The apparent molar absorption coefficient is 1.0 x 10(3) L/(mol cm). The method has been successfully applied to the determination of thiamazole in pharmaceutical samples with satisfactory results, and recoveries are in the range of 99.6-100.6%. (C) 2011 Elsevier B.V. All rights reserved.