Estimation of iodine in salt fortified with iodine & iron

The National Institute of Nutrition (NIN), Hyderabad has developed double fortified salt (DFS) containing both iodine and iron to control the twin problems of iodine deficiency disorders (IDD) and iron deficiency anaemia (IDA). When the iodine content of DFS was estimated by the conventional iodometric titration using sulphuric acid (H(2)SO(4)), problems such as wide variation between duplicate analysis and under/overestimations of iodine content were encountered, which led to inconsistent results. This study was undertaken to develop a modified method for the estimation of iodine in DFS so as to get reliable iodine content of DFS.

A modified method was developed using orthophosphoric acid (H(3)PO(4)) and the sensitivity of the method was confirmed by estimating the iodine content of potassium iodate (KIO(3)) standard at different concentrations of iodine (0 to 100 ppm). The iodine content of DFS and iodized salt (IS) from local market and factory was estimated by the modified method as well as the conventional iodometric titration and the results were compared.

The pH of DFS was acidic. The time gap between the additions of acid and potassium iodide (KI) played a crucial role in getting the actual iodine content of DFS. The H(2)SO(4) and ferrous sulphate (FeSO(4)) interfered with the estimation of iodine in DFS resulting in underestimation or overestimation of iodine. Modified method (H(3)PO(4)) produced consistent and reliable iodine content of DFS. Both H(2)SO(4) and H(3)PO(4) gave same results when tested with KIO(3) standard, Reference salt and IS (both experimental and purchased from local market). Actually 0.50 ml of 1 per cent KI was sufficient to estimate the iodine content of DFS or IS.

The results of the present study showed that the conventional method using H(2)SO(4) was not suitable for the estimation of iodine in DFS. The modified method using H(2)PO(4) was ideally suited for the estimation of iodine in DFS. Also, iron from DFS did not interfere during estimation of iodine by this method. As both the conventional and the modified methods gave the same results for the iodine content of IS, it is practically prudent to use the modified method (H(2)PO(4)) for both DFS and IS instead of following one method (H(3)PO(4)) for DFS and another (H(2)SO(4)) for IS. The quantity of KI is also reduced and the order of additions of reagents is changed in the modified procedure.