Determination of iodine in plant materials

The determination of iodine in plant materials was examined by use of chromium trioxide as an oxidant in wet digestion followed by the distillation of iodine reduced from iodate in the presence of phosphorous acid as a reductant. The recommended procedure was as follows: 1 g of dried seaweeds was decomposed to carbon dioxide by heating with 5 g of chromium trioxide and 20 ml of sulfuric acid in a flask, and the contents was heated to 2200C to decompose the excess chromium trioxide to tervalent chromium. After cooling the contents of the flask in air, iodate was reduced to iodine by phosphorous acid and then iodine produced was distilled in 10 ml of 10% sodium hydroxide solution. At the distillation stage, 2 g of phosphorous acid was used with a small amount of sodium nitrate, because nitrous acid produced from nitrate ion in the presence of phosphorous acid accelerated the distillation of iodine. By the results of experiments using 125I as a tracer, the recovery of iodine from dried seaweeds (1 g) was found to be (97 -- 99)%. (author)