Monitoring iodine content in iodized salt is necessary for program effectiveness. Iodometric titration, the standard WHO method of measurement, requires technical skills and a central laboratory. Rapid test methods detect iodine presence but not quantitatively. The University of Notre Dame developed a disposable Paper Analytic Device, “saltPAD”, to quantify iodine in iodized salt, using mobile technology to record results. Researchers externally validated the overall performance of the saltPAD against iodometric titration for potential use in programs.
Iodized salt samples (n=322) of various particle sizes, purities, iodine concentrations and pH levels, were tested in duplicate for iodine content using saltPAD and iodometric titration. Two analysts interpreted photographic images of the saltPAD. Results were compared against iodometric titration, capturing imprecision and agreement between the methods.
94% of the results within the 0-<15 ppm range were in agreement (<1% bias), while 88% were correctly categorized within =15 to 55 ppm range, but showed a negative bias (-9 %). Samples in the =35-55 ppm range had an average error of 25% (-12% bias). In 74% or more of the analyses, the imprecision for both the saltPAD and iodometric titration was =5 ppm, with little variation between analysts (r=0.95).
The saltPAD can distinguish between inadequately (< 15 ppm) and adequately (=15 ppm) iodized salt. By improving accuracy for concentrations above 35 ppm, testing salt samples with high alkalinity, and extending the shelf life, the saltPAD could be useful for providing immediate, semi-quantitative results to supplement iodine coverage surveys and national iodization programs.