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Determination of Methimazole in Pharmaceutical Preparations using an HPLC Method Coupled with an Iodine-Azide Post-Column Reaction

Abstract A simple and reliable high performance liquid chromatographic (HPLC) method with iodine-azide post-column reaction as a detection system has been developed and validated for determination of methimazole in tablets. A chromatographic separation was achieved on a C18 column with a mobile phase consisting of acetonitrile, water, and 2.5% sodium azide solution (pH 5.5) with isocratic elution (20:30:50, v/v/v). The detection is based on spectrophotometric measurement of the residual iodine (λ = 350 nm) from the post-column iodine-azide reaction induced by methimazole, after mixing an iodine solution containing iodide ions with the column effluent containing azide ions and methimazole. Obtained chromatograms for methimazole showed negative peaks as a result of the decrease in background absorbance. The method developed for methimazole was linear over the concentration range of 0.2–2 µmol L−1. The method is accurate and precise (relative standard deviation, R.S.D. < 4%). The detection limit (defined as S/N = 3) was 0.18 µmol L−1 (3.6 pmol injected amount) for the described compound. The elaborated method was applied to determine methimazole in tablets.