Simplified Bromide Determination in Blood and Urine*

In 1938 Brodie and Friedman (1) published a method for the determination of bromide in tissues and biological fluids. Tissues, serum, urine, or spinal fluid was dried and then fused with sodium hydroxide on a sand bath and the melt containing the bromide was dissolved in water. The use of bromide as a measure of the extracellular fluid was demonstrated by Brodie, Brand, and Leshin (2,3). In the present paper, a method for determining bromide in the serum and the urine is reported. The fusion, with subsequent solution of the melt and transferring, is the most, complicated and time-consuming step of the original method. A study was made of different protein precipitants to substitute for the fusion, and the use of trichloroacetic acid was found to give quantitative recoveries of added bromide to serum. The filtrate from trichloroacetic acid is treated essentially as in the original method. The bromide is oxidized to bromate by sodium hypochlorite buffered with acid phosphate. The excess hypochlorite is reduced by sodium formate and the addition of iodide to the bromate in acid solution results in the liberation of 6 equivalents of iodine. The iodine is then titrated with standard thiosulfate solution. A simplified and accurate method for the determination of bromide in urine is also included in this communication. The bromide and chloride are precipitated from urine as the silver salts in the presence of nitric acid (4). The supernatant fluid is removed, the halides are suspended in acid phosphate solution, and the bromides oxidized as for serum. ReagentsTrichloroacetic acid, 10 per cent. Sodium dihydrogen phosphate (NaH2P04 * HzO), 40 per cent. Sodium hypochlorite, 1.0 N in about, 0.1 N NaOH. Pass chlorine gas with constant stirring into a solution containing 44.8 gm. of NaOH in 1000 ml. of solution. The alkalinity is tested at intervals by destroying the hypochlorite in 1 ml. of solution with 2 ml. of 3 per cent hydrogen peroxide, diluted to 10 ml. and titrated with 0.1 N HCI. The titer should be between 0.8 and 1.2 ml. The reagent is stable for several weeks in the refrigerator.