Determination of Total Iodine in Infant Formula and Adult/ Pediatric Nutritional Formula by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS): Collaborative Study, Final Action 2012.15.

A collaborative study was conducted to determine total iodine in infant formula and adult/pediatric nutritional formula by inductively coupled plasma-MS (ICP-MS) using AOAC First Action Official Method(SM) 2012.15. The purpose of this study was to evaluate the method's intralaboratory and interlaboratory performance and submit the results to AOAC INTERNATIONAL for adoption as a Final Action Official Method for the determination of total iodine in infant formula and adult/pediatric nutritional formula. Upon providing acceptable results for practice samples National Institute of Standard and Technology (NIST) Standard Reference Material (SRM) 1849a and a low-fat adult nutritional powder, 13 laboratories analyzed seven various infant and adult nutritional products including a blind duplicate of each. Products were chosen with varying levels of iodine and included low-fat, soy-based, and milk-based formulas and NIST SRM 1849a. Random identification numbers were assigned to each of the seven fortified test materials. Digestion of the test samples occurred using a potassium hydroxide solution in an oven or open-vessel microwave system. Iodine was stabilized with ammonium hydroxide and sodium thiosulfate after digestion. The solutions were brought to volume followed by filtration. The filtrates were then analyzed by ICP-MS after dilution. Results for all seven test samples met all the AOAC Standard Method Performance Requirements (SMPR(®) 2012.008) guidelines. The RSDr ranged from 0.77 to 4.78% and the RSDR from 5.42 to 11.5%. The Horwitz ratio (HorRat) for each result was excellent, ranging from 0.35 to 1.31%. The results demonstrate that the method is fit-for-purpose to determine iodine in infant formula and adult/pediatric nutritional formula.