Development of a green and efficient method for determination of iodine in mineral dietary supplements

In this work, an analytical method for iodine determination in mineral dietary supplements was developed. Microwave–induced combustion (MIC) was evaluated as sample preparation method and iodine was determined by ion chromatography (IC). It was possible to decompose up to 800 mg of supplement using 20 bar of oxygen and 6 mL of a diluted alkaline solution (200 mmol L-1 NH4OH). Accuracy was evaluated by analyte recovery tests using standard solution, and the recoveries ranged from 94 to 106%. Relative standard deviations (RSDs) were always lower than 9% and the limit of detection was 2.2 μg g-1. The proposed method was applied for the analysis of dietary supplements of variety brands containing different dosages of iodine (from 100 to 1250 μg g-1, according to the manufacturers). Iodine concentrations for all analyzed samples presented statistical differences (Student’s t-test, 95% of confidence level, n=10) within values reported by manufacturers, when 30 tablets/capsules were homogenized and analyzed by the proposed method. An additional study was performed based on the uniformity dosage units assessment of the United States Pharmacopeia. In this evaluation, the tablets/capsules were digested individually and the RSDs were up to 42%, which demonstrate possible problems on the uniformity dosage units and the importance of the dietary supplements quality control. The proposed method presents a high throughput, a suitable accuracy and precision and allows the use of diluted solutions according to green chemistry.