Inductively Coupled Plasma-Mass Spectrometric Determination of Iodine in Food Using Tetramethyl Ammonium Hydroxide Extraction-Results from a U.S. Food and Drug Administration Level 3 Interlaboratory Study.

Background: The performance of U.S. Food and Drug Administration (FDA) Elemental Analysis Manual (EAM) 4.13 method (Inductively Coupled Plasma-Mass Spectrometric Determination of Iodine in Food Using Tetramethyl Ammonium Hydroxide Extraction) was tested in an interlaboratory study. Objective: The aim of the study is to demonstrate that the FDA EAM method 4.13 is applicable for the analysis of food and multivitamins. Methods: Six collaborators participated in the study using four different models of inductively coupled plasma-mass spectrometry instruments. The method evaluation included determination of the limits of detection and quantification, analysis of National Institute of Standards and Technology standard reference materials (SRMs), unknown samples, blinded SRMs, and fortified analytical portions by all six collaborators. The samples were chosen to represent all sectors of the AOAC food triangle and additionally included pet food and multivitamin tablets. Results: The repeatability and reproducibility ranges were 1.8-11.4% and 3.6-13.7%, respectively; the calculated HorRat values were in the 0.17-1.18 range; and 174 of 175 SRM analyses had z-scores <2 and fortified analytical portion samples with recoveries of 102-105%, indicating acceptable method performance. Conclusions: The study supports a Level Three Multilaboratory Validation according to FDA Food and Veterinary Program Guidelines performed by six collaborators using six certified reference materials and nine unknown samples. Highlights: The method is applicable for quantification of the total extractable iodine in food and multivitamin dietary supplements.