Reliability of analytical results from iodine rate-monitoring in salt for human consumption: methodology validation and measurement uncertainty

Abstract

Salt for human consumption is used to increase iodine intake and prevent Iodine Deficiency Disorders. This worldwide practice is recommended by the World Health Organization and monitored by government programs. The determination of iodine content in salt, added as potassium iodate, is a classic method used in national monitoring. Despite being the most common iodine-quantification method, it is not documented in publications to support Sanitary Surveillance initiatives. The purpose of this study was to evaluate the effectiveness of iodine determination in salt, added as potassium iodate, by iodometric titration and calculate its measurement uncertainty to investigate the reliability of the results. The results need to be accurate and precise to standardize monitoring programs. The study was conducted in eight concentrations, from 2 to 100 mg/kg. The method is robust. It features selectivity without matrix interference, linearity (r2 = 0.99998) through the range of values studied, detection limit set by visual evaluation at 1 mg/kg, quantitation limit of 2 mg/kg, 98–101% recovery, relative standard deviation ≤ 7.15%, inter-operator reproducibility as shown by a repeatability limit of 0.55 mg/kg, and intermediate precision (p = 0.41). The measurement uncertainty was set at 0.93 mg/kg with a 95.45% confidence level.