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/L H2SO4 solution to form a product with phosphorus–molybdenum heteropoly acid ([H2PMo12O40]−). Then [H2PMo12O40]− is deoxidized to form phosphorus molybdenum blue (H3PO4·10MoO3·Mo2O5) by thiamazole. The amount of thiamazole can be determined based on the absorbance of phosphorus molybdenum blue (λmax = 710 nm). A good linear relationship is obtained between the absorbance and the concentration of thiamazole in the range of 0.035–70 μg/mL. The equation of the linear regression is A = 0.03384 + 0.00834c (μg/mL), with a linear correlation coefficient of 0.9990. The apparent molar absorption coefficient is 1.0 × 103 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%.

Graphical abstractIn 0.30 mol/L H2SO4 solution, PO43− reacts with Mo7O246− to form a product with phosphorus–molybdenum heteropoly acid, which is deoxidized to form phosphorus molybdenum blue by the sulfhydryl group of thiamazole. The amount of thiamazole can be indirectly determined by the absorbance of phosphorus molybdenum blue (λmax = 710 nm).Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Thiamazole is determined by phosphorus molybdenum blue spectrophotometry. PO43− reacts with Mo7O246− to form a product with [H2PMo12O40]−. [H2PMo12O40]− is deoxidized to form phosphorus molybdenum blue by thiamazole. The absorbance of phosphorus molybdenum blue is measured at 710 nm.