A simple method for determining serum copper.

The determination of serum copper is of value in a number of metabolic studies, particularly in the investigation of the anemia of chronic infection. Presented here, together with illustrative data, is a method for determining copper in serum, based on the direct extraction of copper carbamate from serum with isoamyl alcohol. Burch et aa. in their method for serum iron have demonstrated that such direct extractions with immiscible solvents are satisfactory (1). Simplicity of methodology is the chief advantage of this procedure; steps such as dry ashing, wet oxidation, and multiple extractions with trichloroacetic acid are eliminated. Sodium diethyldithiocarbamate, the reagent used to react with copper in this procedure, gives colored complexes with a number of heavy metal cations (2). In biological material, however, iron is the chief interfering substance. This interference of iron is satisfactorily eliminated by developing the copper carbamate complex in an ammoniacal solution containing pyrophosphate and having a pH 9 or greater (2-4). The color intensities of other interfering metals such as nickel and cobalt are weight for weight only one-twentieth to one-thirtieth as great as that given by copper (5). Because the concentration of these ions (Ni and Co) in serum is of such a relatively low order, their interference is negligible. The final color of the extracted copper carbamate is the result of three contributing components: serum copper, copper present as impurity in the reagents, and substances other than copper carbamate which are extracted from serum by isoamyl alcohol. Copper carbamate is soluble in a number of organic solvents in addition to isoamyl alcohol, namely ethyl ether, amyl alcohol, amyl acetate, bromobenzene, and carbon tetrachloride (2). Of these reagents, only ethyl ether and isoamyl alcohol were tried as extractives. The latter proved to be more satisfactory.