Improvement in the Reliability of AOAC Official Method 2012.15 for Iodine

Background: Reliable measurements of iodine are essential for ensuring the quality of infant formula. The AOAC Official Method 2012.15 for iodine tends to produce higher results in the presence of carbon remaining in the final test solution after digestion with alkaline dissolution. This is partly because of the lack of countermeasures for signal enhancement induced by coexisting carbon in Method 2012.15. Objective: To obtain more reliable values for infant formulas, we undertook an experiment. Methods: We modified the protocol by adding carbon in the form of methanol to both the standard solutions and the final test solutions. Comparisons of the enhancement factor for iodine-127 were used to find the optimized concentration of methanol from 0-10%. Results: Optimization of the additional carbon showed that a 5% methanol minimum was necessary for a constant ratio of iodine. The results exhibited good linearity (coefficient of determination >0.999), and the LOQ was 0.19 μg/100 g for the reconstituted final product with a methanol concentration of 5%. The intermediate precision RSD was <3.76%, and the recovery factor was 97.5-104.2% for infant formula distributed in several countries and a special formula distributed in Japan. Conclusions: This demonstrates that 5% methanol, when added to standard and final solutions, acts as an effective matrix matching agent. Highlights: This modified method produces more accurate iodine quantification in infant formulas and special formulas in which there is incomplete digestion of the matrix.