Field Tests for Iodate in Salt

Abstract

Commercially available field test kits for the determination of iodate in salt were tested to evaluate their performance and to devise improvements in their range and accuracy. Dropper tests based on the blue colour of the starch-iodine complex formed with iodine released by excess potassium iodide gave rapid qualitative indication of the presence of iodate. Because of the dark colour of the complex, the tests were found to be quantitative over only a limited range, typically 0 to 20 μg of iodine per gram of salt. We have developed methods for improving the reliability and colour reproducibility of these types of kits. Instructions for producing reliable kits of this type with improved colour reproducibility are presented. Improved qualitative tests in the range of 0 to 50 μg/g were obtained with a simple liquid-phase colourimetric system, based on the same chemistry. A field test kit was developed and tested in laboratories in India and Zimbabwe, as well as in our laboratory in Toronto. the test gave reproducible results, comparable to those of titration, with a typical standard deviation of ± 5 μg/g. the range of measurements can be extended to 100 μg/g by dilution. Instructions for preparing these kits are presented.