The determination of iodin in iodin metabolism

Abstract

The organic material for iodin analysis is dried, mixed with and covered with CaO to render it alkaline and reduce the rate of combustion, and burned in pure oxygen in a large combustion tube with the end narrowed and bent downward for about 50 cm. The first third of this narrowed portion is covered with a thin layer of asbestos fibers to protect it from a lead coil through which cold water runs. The middle third is water-jacketed. The lower third dips into an absorbing apparatus filled with NaOH solution. The greater the amount of CaO mixed with the unknown material, the greater amount of iodin remains in the ash. The alkaline solution from the absorption apparatus is evaporated to 10 c.c. after adding to it the rinsings of the combustion tube. The ash is ground with water or the solution from the absorption apparatus in a ball mill and the extract is evaporated to 10 c.c. The solution is acidified until P_H = 1 and placed in a 12 c.c. separatory funnel and 0.1 c.c. of 0.1 N arsenius acid added, and allowed to remain for one-half hour to reduce any iodate to iodide. Then 0.1 c.c. of 5 per cent. sodium nitrite is added to oxidize the iodide to iodin which is extracted with 1 c.c. of CCl₄. The partition coefficient of iodin between CCl₄ and the aqueous solution is about 86, but varies with conditions. The iodin in CCl₄ is run into a 1 C.C. glass stoppered bottle and centrifuged to remove water droplets. The iodin is determined calorimetrically with a Bausch and Lomb Biological calorimeter specially made with cups holding 1 C.C. at 2 cm. depth, against a standard solution of pure iodin in CCl₄ (1 mg. in 10 c.c).