The Determination of Thiocyanate in Serum after the Administration of Its Salts

The present interest in the determination of thiocyanate in serum, following the injection or ingestion of its salts, is twofold. First, in order to control hypertension by administering thiocyanate, the dosage must be regulated by frequently checking serum levels, as pointed out by Barker (1) and Wald, Lindberg, and Barker (2). Secondly, the determination of extracellular fluid, as originally described by Crandall and Anderson (3), and later modified by Lavietes, Bourdillon, and Klinghofer (4), involves the measurement of the concentration of thiocyanate in serum. This method enjoys a wide-spread use. Schreiber’s procedure (5) for the quantitative detection of this compound in serum has been adopted with minor modifications by many workers in these two fields (14, 6). In general, the serum containing thiocyanate is treated with trichloroacetic acid to obtain a clear, protein-free filtrate. To the latter, acid ferric nitrate is added, and the resulting orange-red color examined either calorimetrically or photometrically. In this communication a method is described whereby the determination of thiocyanate is carried out directly upon serum merely by addition of acid ferric chloride. Since the preliminary precipitation of protein is thus obviated, the analysis is not only shortened but greatly simplified. Furthermore, the actual examination of a small sample of serum is quickly performed in the microphotoelectric calorimeter of Evelyn and Cipriani (7, S), with the plunger type of absorption cell of Evelyn and Gibson (9). As Gibson and Evelyn (10) have shown in the case of “Evans blue” dye, this instrument is fully as reliable as the spectropho-