Iodine determination in food samples using inductively coupled plasma isotope dilution mass spectrometry

Two different sample treatment methods are used in connection with inductively coupled plasma isotope dilution mass:spectrometry for accurate and precise determinations of iodine traces in food samples. I-129-enriched iodate is applied as a spike compound for the isotope dilution step. Extraction of iodine by tetramethylammonium hydroxide (TMAH) solution at high temperatures in a closed vessel is one of the sample treatment methods. The other one is a complete decomposition of the sample with a mixture of perchloric acid and nitric acid using microwave assistance. By analyzing different certified reference materials (three milk powders with different iodine levels, BCR CRM 63, 150, and 151; bovine liver BCR CRM 185), the accuracy of ICP-IDMS with both sample treatment methods could be demonstrated. The relative standard deviation was typically in the range of 0.6-2.8% for iodine concentrations between 0.1 mu g g(-1) and 5 mu g g(-1). The detection limit was 8 ng g(-1) using sample weights of 0.8 g. In a round robin test, using two different types of infant food samples, the results of the two ICP-IDMS methods and of an ICP-MS method without the isotope dilution technique, but applying the TMAH extraction procedure, agree very well with:the mean of results of all participating laboratories also using ICP-MS/TMAH. However, the ICP-IDMS-method is faster, more precise, widely independent of matrix effects, and, therefore, relatively accurate, which makes-this method especially attractive for use as a routine method.