Iodine determination in mineral water using ICP-MS: method development and analysis of brands available in Israeli stores

Reliable iodine determination in drinking water samples has gained importance in the last few decades, mostly due to intensive use of both desalinized water that lacks several important nutritional elements, and bottled mineral water. ICP-MS is a sensitive, high-throughput method for iodine determination that must be performed under alkaline conditions because of the volatile nature of some iodine species. However, in water samples with high pH (>10), slow precipitation of calcium (Ca) and/or magnesium (Mg) carbonates leads to clogging of the ICP-MS nebulizer. We propose preventing this precipitation by adding the chelating agent ethylenediaminetetraacetic acid (EDTA) at 0.1% to a 2% ammonium hydroxide matrix. This concentration of EDTA sufficed for most drinking water samples studied, as long as a 1:1 molar ratio of EDTA to Ca+Mg concentration in the water was maintained. The limit of quantitation of the developed method for iodine was <0.1 µg L-1. The average iodine concentration in various brands of bottled mineral water sold in Israel was relatively low (7.67 ± 6.38 µg I L-1). Regular consumption of either desalinated water or bottled mineral water may induce iodine deficiency in Israeli consumers. Therefore, continuous follow-up of the iodine status in both tap and bottled water is strongly recommended.