The Colorimetric Estimation of Protein-bound Serum Iodine*

The following procedure is an adaptation of the precipitation and digestion procedures described by Man, Smirnow, Gildea, and Peters (1) and Riggs and Man (2) to distillation in the Chaney apparatus (3) as modified by Riggs’ and application of photoelectric micro calorimetry to the quantitative assay of iodate instead of the usual starch-iodine titration. This procedure permits satisfactory analyses to be made on 4 cc. of serum. Reagents-The reagents for precipitating the serum proteins were prepared according to the directions of Man, Smirnow, Gildea, and Peters (1). All other reagents were prepared according to the directions of Riggs and Man (2) as outlined by Salter (4). “Water pump” dry nitrogen (Air-Reduction Sales Company). The solutions of arrowroot starch and of sodium bisulfite (NaHSOs, Merck, c.P.) were prepared freshly at monthly intervals. Special ApparatusRiggs” modification of the distillation apparatus originally described by Chaney (3) (see Fig. 1). The distillation flask of this apparatus is used for the digestion of the sulfuric acid solution of the serum proteins. The central section of the apparatus (i.e. that portion lying between Joints A and B) should be washed with chromic acid cleaning solution followed by several rinsings of distilled water between runs. No stop-cock grease is used on the glass joints, but a trace may be used on the stop-cock attached to the “trap” and on the stop-cock of the dropping funnel. Care should be taken to prevent any contamination of the distillation mixture with the lubricant. Evelyn photoelectric micro calorimeter, equipped with 2 cc. cells and a filter having maximum light transmission at 620 rnp (range 525 to 660 mp). 911 apparatus used must be scrupulously clean.