The Determination of Zinc in Biological Materials*

The occurrence of zinc in biological materials is no longer a matter of conjecture. The presence of zinc in all plants and lower animals so far studied, as well as its occurrence not only in the whole body of the higher animals but in the individual tissues such as liver, kidney, muscle, etc., has been established beyond doubt. In 1926, Lutz (1) reviewed very completely our knowledge concerning the occurrence and distribution of this element in biological materials. A study of the figures presented in this review reveals that the great discrepancies in the values obtained by different workers for like materials can only be partially accounted for by variations in the zinc content of the samples; the greater part of the differences must be due to the lack of standard methods of analysis. Workers have suggested various functions of zinc in the metabolism of plants and animals. A review by Drinker and Collier (2), however, shows that no specific activity has as yet been ascribed to this element. The lack of available methods for the accurate estimation of zinc seems to be the limiting factor in the continuation of this work. In our attempts to utilize certain of the published methods for the estimation of zinc in plant and animal tissues, considerable difficulty was encountered. The methods which gave fairly accurate results in our hands were exceedingly time-consuming. With other methods we were unable to obtain consistent values. Attempts to modify parts of various methods in order to adapt