Microscale assessment of iodate fortificant in food-grade salt using the potassium iodide/polyvinyl alcohol colorimetric reagent

Abstract

A rapid and straightforward spectrophotometric measurement of iodate in food-grade sodium chloride was developed based on the formation of a purple-red polyvinyl alcohol-iodine complex monitored at 490 nm. The conditions that influence the colorimetric reactions were optimized using a univariate approach. The method exhibited optimum results using 2% polyvinyl alcohol, 10 mM KI, and 0.5 M phosphoric acid. A matrix-matched calibration curve was prepared to eliminate interference due to the presence of NaCl and to provide a direct reading of iodate concentration in salt from the absorbance reading. Under optimum conditions, a linear calibration plot was observed from 5 to 140 mg iodate per kilogram (r = 0.9931). The method exhibited a sensitivity of 6.8 × 10−3 (mg iodate per kg of salt)−1 with a detection limit of 0.61 mg kg−1. The method was applied in actual samples, and the results agreed well with the titration method at a 95% confidence level using a paired t-test. The method supports the green analytical method as evaluated using Green Analytical Procedure Index (GAPI) and Analytical Eco-scale.