Abstract
A method for the determination of diodrast and inorganic iodide iodine in blood and urine was presented previously. 1 The principles involved were acid permanganate digestion of the sample with oxidation of iodine to iodate, nitrite reduction of the permanganate, destruction of excess nitrite with urea, and titration of the iodate with thiosulphate in an excess of potassium iodide. This procedure could be carried out either by hand heating of the individual tubes over a micro burner or by heating a number of tubes in a boiling water bath. The digestion of individual samples by hand yields accurate results but requires the constant attention of the analyst. The water bath digestion, however, involves some error, particularly in the digestion of plasma filtrates at high iodine levels, and it is sometimes more difficult to remove all of the permanganate because some manganese dioxide adheres firmly to the walls of the tubes. It is shown here that with an alkaline permanganate digestion these difficulties with the water bath heating are eliminated.
With an alkaline digestion more permanganate must be used, and a longer heating period allowed than with the acid digestion. In order to keep down the volume of the digest at time of nitrite treatment and at subsequent titration, preliminary evaporation of filtrate samples is carried out.
Procedure. Reagents: 13% trichloracetic acid (A.R.), 72% sodium hydroxide (A.R.), approximately 0.4 M potassium permanganate, 4 N sulfuric acid, 1.0 M sodium nitrite, 5 M urea, granulated potassium iodide, 1 % starch, 0.0005 N sodium thiosulfate or 0.0025 N sodium thiosulfate.
Apparatus: circular test-tube rack, water bath, 18×150 mm test tubes, dropping bottles, burette calibrated to 0.01 cc or 0.05 cc.
In preparing the potassium permanganate make a 7% solution, boil for 5 to 10 minutes and let stand for at least 24 hours.
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