Field Tests for Iodide in Salt

Abstract

Rapid field tests for the determination of iodide in salt were developed, based on the oxidation of iodide to iodine and reaction of the released iodine with starch to produce a coloured complex that could be visually related to the iodide content of the salt. Potassium iodate and ferric chloride were used as oxidizing agents in the two versions of the test that were examined in detail. the reaction with ferric chloride gave a test with a wider useful concentration range. It had the added advantage of not producing false readings for iodine by reacting with reducing agents that were present in the salt as natural impurities or as a result of fraud. A simple test kit suitable for field use was developed and tested with iodized salts produced using salts from Canada and Ecuador. the kit results were compared with results obtained by neutron activation analysis using the SLOWPOKE nuclear reactor facility of the University of Toronto and by standard iodometric titration. the test kits readily analysed for iodine levels between 0 and 50 ppm, with an accuracy of ± 10 ppm and a reproducibility of ± 5 ppm. Inexpensive rapid tests using these kits may be useful in monitoring iodine levels in areas where salt iodization is based on potassium iodide, because of the presence of impurities in the salt supply that reduce the stability of the usual iodizing agent, potassium iodate.