Senior Technical Advisor USAID Advancing Nutrition Arlington, Virginia
Iodometric titration is the reference method for measuring iodine concentration in salt. The process depends on a chromogenic reaction whose color intensity is proportional to the iodine concentration. The chromogen (color compound) can be measured in a photometer. For years, several commercial field photometers have used this principle.
In this study, we compare the performance and cost of three field devices (iCheck Iodine, WYD iodine checker, iReader), one laboratory device (UV-Vis spectrophotometer), and titration for measuring iodine of iodized salt samples prepared in the same way.
All chromogenic methods provided acceptable and comparably accurate results within the range of 10 to 60 parts per million (ppm) iodine. All methods but iCheck were able to determine iodine content up to 90 ppm without need of dilution. However, only the i-Reader and the UV-Vis were able to determine iodine contents lower than 10 ppm. The cost per sample was lowest for WYD, UV-Vis, and iReader ($0.99-1.17), intermediate for titration ($1.87), and highest for iCheck ($9.20). The time taken per sample was lowest for iReader (8 min) and highest for titration (16 min), with the others falling in the middle of the range.
Over the long-term, the use of a UV/Vis spectrophotometer is a sustainable option for measuring iodine in salt in laboratories of low- and middle-income countries. Portable field photometric devices like iReader and WYD methods are valid alternatives for a simple and low cost determination at the site of production or at national borders upon entry of iodized salt.