Precipitation by trichloroacetic acid as a simplification in the determination of zinc in blood and its components.

Recent studies have established the importance of zinc as a biological constituent in human blood. Normal zinc levels for human whole blood, plasma, erythrocytes, and leucocytes have been established (1) ; significant deviations from the norm occur in leucemia and pernicious anemia, and, possibly, in sickle-cell anemia (24). Zinc concentration is considered an expression of the carbonic anhydrase content of erythrocytes (5). The method employed for zinc analysis in these earlier studies was accurate for samples of biological material containing between 2 and 30 y of zinc, with a standard error of about f10 per cent (6). Its usefulness for the study of blood is limited by the costly and specialized equipment necessary and by the small number of samples which can be analyzed daily. These objections to the earlier method have now been obviated by protein precipitation with trichloroacetic acid, making zinc quantitatively available for measurement with diphenylthiocarbazone. Zinc determinations, after ashing at 500” (6), have also been made on all samples so studied.