A method for the determination of copper in blood serum.

The demonstration that copper is transported in the serum (1) makes available a means of studying copper metabolism and gives rise to the necessity of having a simple and accurate method which can be applied to the measurement of a large number of samples. The purpose of this paper is to present such a method. Sodium diethyldithiocarbamate has been found t,o be a sat’isfactory and sensitive reagent for the determination of copper. Callan and Henderson (2) discovered that when this substance was added to a solution of copper a golden brown color was produced. McFarlane (3) found that the colored copper salt could be rapidly and quantitatively extracted from aqueous solution by amyl alcohol and that the color was intensified in the organic solvent. The depth of color was reported to be directly proportional to the amount of copper present, provided the range of copper concentrations was not too great. The color complex is stable for at least 2 hours and the pH of the solution has little effect on the color intensity between pH 5.7 and 9.2. Iron gives a brown color with the reagent and is the only substance in biological ash which is known to interfere significantly. However, when sodium pyrophosphate is added, iron pyrophosphate is formed and this compound does not react with the carbamate, whereas the reactivity of the copper is unaffected (3,4). Locke, Main, and Rosbash (5) prepared a protein-free filtrate of serum by precipitating the proteins in the cold with trichloroacetic acid and determined the copper content of the filtrate with the carbamate reagent. Recoveries of added copper were not reported. Tompsett (6) demonstrated that the whole of the serum copper is present in such a filtrate and is present in such a form that it can be determined directly with carbamate. Using such a procedure, he obtained excellent recoveries and the results compared closely with those obtained by ashing. The observations of Yoshikawa, Hahn, and Bale are not in agreement (7). Using radioactive copper, they found that nearly all of the copper in plasma is bound in some manner to