An Improved Dithizone Method for the Determina- Tion of Small Quantities of Zinc in Blood

The study of zinc metabolism in experimental animals and humans is dependent upon a reliable analytical method. Numerous methods, gravimetric, turbidimetric, and calorimetric (l), have been tried and found wanting. Fischer (2) first introduced diphenylthiocarbazone (dithizone) for the analysis of metals with relation to industrial processes. This organic dye combines with a number of the heavy metals (Sandell (3)). The combination is selective for any one metal, depending upon the pH of the solution containing the metals, and the presence of salts which form complexes with other metals in solution. It was not until 1937 that Fischer and Leopoldi (4) adapted the dithizone method to the analysis of inorganic zinc. Holland and Ritchie (5) and Cowling and BIiller (6) used this dye for zinc analyses in plants, and Hove et al. (7) in the measurement of carbonic anhydrase. The procedure employed by these authors, however, involved a preliminary extraction of other metals, principally copper, and a final extraction of zinc. Gettler (8) simplified the method by the use of a buffered solution of complex-forming salts, obviating the preliminary separation. We have further refined the method to obtain greater accuracy in the analysis of the zinc content of samples of whole blood, plasma, erythrocytes, and leucocytes and samples of tissue. Samples of the size which can be practicably obtained may contain as little as 1 to 5 y of zinc. Diphenylthiocarbazone has the following structural formula: