A Paper Test Card Provides Quantitative Measurement of Iodate to Improve Quality Control of Iodized Salt in Low-resource Settings

Abstract

Objectives: Monitoring iodine content in iodized salt is necessary for program effectiveness. Iodometric titration is the most precise method but requires skills, facilities, and reagents. The WYD Iodine Checker® and Bioanalyt iCheck® are quantitative, but are expensive, require reagents and electrical power. Iodometric titration has been adapted onto a paper test card to quantitatively measure iodate in iodized salt in low-resource settings. A cell phone is used to evaluate test results. Researchers internally validated the test cards to demonstrate accuracy and conducted a field test to demonstrate applicability for quality control in factory settings. Methods: For each sample, 3 drops of a 1:5 salt-to-water dilution were placed onto the test card and mixed for 3 minutes before taking a cell phone image. Images were analyzed against a calibration curve. Two researchers internally blindly validated the test cards against titration at a university lab in Indiana, USA. The field test was performed by a quality technician in a salt factory in Mombasa, Kenya. Results: During internal validation, 78 of 100 samples ranging from 0-75 ppm iodate analyzed were within 20% of the titration result. In the field factory, 24 of 32 samples ranging from 19-55 ppm iodate analyzed by the technician were within 20% range of titration. The technician was trained within 30 minutes and carried out 24 analyses in 3 hours, compared with 15 titrations in 3 hours. Conclusions: The paper test card offers a rapid field-friendly method with sufficient accuracy to use for quality control of iodized salt.