Determination of Zinc in Biological Materials

Several different techniques have been utilized to measure the trace amount of zinc in biological materials. The chemical method is commonly used and has been attempted in histochemical studies on zinc. Some chemical methods will thus be briefly mentioned. Fischer, Hellmuth and Leopoldi (1936) used a method by which zinc is extracted by diphenylthiocarbazone (dithizone) and then colorimetrically determined. Modifications and improvements of this method without greater changes of its original principles are described by several authors e. g. Vallee and Gibson (1948), Vikbladh (1950), Berfenstam (1952), Weitzel and Fretzdorff (1953) and Koch and Smith (1956). The same principles have been used in studies for histochemical determination of zinc, Okamoto (1942 and 1944, see Okamoto et al. 1951). The method, however, was shown to have two main disadvantages. Preservation of the stain is impossible and the staining is not specific for zinc. Mager, McNary and Lionetti (1953) used a special dithizone compound for histochemical zinc de­ termination as they regarded Okamoto's method to be insufficiently specific for zinc. Wolff and Ringleb (1954) injected a specially prepared dithizone solution intravenously in animals. The animals were killed and the zinc stained granula were microscopically determined in frozen-sections from the pancreas. Un­ fortunately the sections faded after some hours. For persons unfamiliar with chemical processes the above mentioned dithizone method is somewhat complicated. The method is laborious and time-consuming and extreme caution must be observed in the manipulation with the different solutions. Banks, Tupper, Watts and Wormall (1954) extracting Zn in bio­ logical materials with dithizone, calculated with a loss of 3—5 °/o Zn during die whole procedure.