Indirect Determination of Methimazole in Pharmaceutical Sample by Discoloration Spectrophotometry Using Fe(III)-Tiron System

A novel method for the indirect determination of methimazole by discoloration spectrophotometry using Fe(III)-tiron system has been established. The various effect factors on the determination of methimazole by discoloration spectrophotometry using tiron-Fe(III) system were investigated in detail. The results showed that by controlling pH=2.8,Fe(III) could be reduced to Fe( II) by hydrosulfuryl(-SH) in methimazole molecule,and then using tiron as chromogenic reagent of Fe(III),and the content of methimazole was determinated indirectly through determinating the surplus content of Fe(III) in the system. The maximum absorption wavelength of chromogenic system was 663 nm, good linear relationship was obtained between AA and the concentration of methimazole in the range of 3.2 similar to 12.8 mu g.mL(-1),the equation of the linear regression was Delta A=-0.1849+57.277p (mg.mL(-1)),with a linear correlation coefficient was 0.9998. This proposed method had been successfully applied to determinate of methimazole in real pharmaceutical.