The Determination of Iodine in Biologic Material.

One of the greatest hindrances to the biochemical study of thyroid function has been the lack of a relatively simple, rapid, and accurate method for the determination of minute amounts of iodine in biological material. In general, the methods proposed have been of two types-those employing dry ashing and those employing wet digestion. The principal objections to the former group lie in the complexity of the procedure, the great length of time required for each determination, the many possibilities for iodine loss during the process, and the danger of incomplete combustion and loss of volatile substances unless an elaborate closed system is used. Pfeiffer (1928) was one of the first to introduce wet digestion for iodine determination. He suggested a procedure based upon the use of concentrated sulfuric acid and hydrogen peroxide to destroy the organic material and simultaneously liberate the iodine which was conducted into an alkaline absorber. The failure of this method to oxidize fats satisfactorily has greatly limited its usefulness. Leipert (1933, 1934) proposed a method for iodine determination which seemed to offer very distinct advantages over any of the earlier procedures. This investigator oxidized the organic matter with chromic acid in the presence of sulfuric acid and a very small amount of cerous sulfate. All of the iodine present is oxidized to iodic acid by this treatment. The iodic acid is then reduced to free iodine by arsenic trioxide and the liberated iodine steam-distilled at a low pressure into an absorber containing sodium hydroxide. After oxidation of the iodine with bromine, the resulting iodic acid is allowed to react with potassium iodide and