Determination of iodine by solvent extractionion-selective electrode method

The ion-selective electrode method for the microdetermination of iodine in environmental sample was investigated. To isolate iodine from substances influencing on electrode method such as sulfide and large amount of alkali used for alkali fusion of the sample, solvent extraction method was utilized. The recommended procedures are as follows : Add 2 ml of sulfuric acid (1 : l) and sodium nitrite solution (1%) to 150 ml of sample solution in a 250 ml separatory funnel and mix throughly. After standing for (2〜3)min, add 15 ml of carbon tetrachloride and shake for 1 min. Transfer the organic phase to a 200 ml separatory funnel. Repeat the extraction of iodine once more with 10ml of carbon tetrachloride and combine with the first extract. After washing with diluted sulfuric acid, transfer the organic phase to a 50 ml separatory funnel containing 10ml of (10^<-2>〜10^<-4>) M sodium bisulfite solution. Shake for 1 min, discard the organic phase, transfer 5 ml of the aqueous phase to a 100ml polyethylene beaker, add 10ml of 10% Phosphate solution, and then determine the iodide concentration by ion-selective electrode method. The recovery of iodine from the 150 ml of supplying water containing (2〜150) μg of iodine was examined for above procedure. The sufficient recoveries were obtained in addition of more than 5 μg. This method was applied to the determination of iodine in lowland rice near an iodine manufacturing plant. Results were well agreed with those obtained by the neutron activation analysis