Determination of Iodine in 5 cc. of Blood

Four and one-half inches of 3/8″ Visking sausage casing is moistened at one end and tied to a frame. Five cc. of blood is run into the open end from a syringe or pipette. The open end is tied and the string attached to the other side of the frame, stretching the casing as much as it will bear, and it is dried 40 min. at 100° in an oven. It is then placed in a screw-feed stoking device with detachable water-cooled platinum tip and burned with 120 cc. of oxygen per minute in a platinum combustion tube heated by gas. The screw feed is advanced 1″ in 20 min. by motor. The combustion products are led through a pyrex absorber containing 3 sintered glass discs and 25 mg. of sodium azide in 10 cc. of water. At the end of the combustion the stoking tube is removed from the platinum tip, which is allowed gradually to heat, the gas flame is turned off, and the absorber contents and ash are transferred to a 100 cc. pyrex still, using 4 cc. N/10 NaOH and 10 cc. H₂O to rinse out. Most of the water is evaporated off while passing a small current of air to prevent bumping, and 3 cc. 6 N H₂SO₄ is introduced into the still. The iodine is distilled over into a 10 cc. receiver containing 1 cc. of bromine water without immersing the tip. The trap is flamed to prevent iodine remaining in drops of water in it. When SO₃ fumes appear in the still, the flame is reduced to 5 mm. and continued for 4 more minutes. After allowing the air to continue until all condensate has run down into the receiver, the tip is washed, volume made to 9 cc, and an air current blown through it in a steam bath for 1/2 hour to remove the bromine. Twelve and one-half mg. KI is introduced, the volume is made to 10 cc, and it is titrated with 0.001 N sodium thiosulfate in a Lochte-Hoover burette with divisions of 0.001 cc. (while rapidly stirred) using an electrometric method for indicating the end-point. Burette readings are plotted against voltage, the curve showing a sharp angle at the end-point. Blanks are run on all the reagents and subtracted from the results. Human blood gave 0.1-0.7γ in 5 cc. On adding iodine, the following was recovered (Table I):