Discussion on national standard for determining iodine ion in salt industry

Abstract

Objective To discuss the national standard method ofGeneral Test Method in Salt IndustryDetermination of Iodine Ionand point OUt an incorrect concentration of sodium hypochlorite(NaClO)solution which is not matched with the concentration of oxalic acid solution being used in the national standard method.Methods The iodine ion in the reference salt was determined step by step as stipulated in the method.During the test,the concentration of the NaClO solution was altered from 5.0%to 0.1%in order to screen the suitable ranges of the concentration of NaClO solution.Results 5.0%NaClO solution was used according to the national standard method,which led to a significant deviation up to 700 ms/kg.The relative errors of the standard iodized salt determination were respectively 2312.0%,185.0%,4.0%,3.3%,-0.6%,-3.0%,-3.3%with different concentration NaClO(5.0%,3.0%,2.5%,1.0%,0.3%,0.2%,0.1%).Conclusion Under the circumstance that the concentration of the oxalic acid solution remains the same.the concentration of NaClO solution must be revised into 0.3%～2.5%in the national standard method to decrease testing errors. Key words: Iodine; Salts; Sodium hypochlorite; Reference standards