Quantitative semiautomated colorimetric determination of thyroid (iodine) in thyroid tablets.

A faster, simpler, more sensitive, and semiautomated method was developed for the analysis of thyroid in individual thyroid tablets and composite samples. The sample is combusted in a Schoniger flask in an oxygen atmosphere, and the liberated iodine is trapped in a dilute sodium hydroxide solution. The solution is acidified with sulfuric acid (1:1), and the iodine is determined colorimetrically using a suitable spectrophotometer equipped with an automated analyzer. The proposed methodology was applied to tablets containing 32.4--324 mg of thyroid. Recoveries ranged from 90.0 to 125.0% of the amount of iodine added as potassium iodide. The proposed method is sensitive to 2.5 ng of iodine/ml.