The rapid determination of calcium in biologic material.

PROCEDURE for the determination of calcium in biologic material, one which would be adaptable to the rapid and accurate analysis of the many specimens encountered daily in the laboratory of a large general hospital, has been the objective of many recent studies. Our interest in this problem has led us to investigate the currently proposed methodology. The critera that we have set for the ideal “routine” procedure were: (1) analysis is to be made directly on the serum, (2) an aliquot of the specimen used should be large enough to be measured with accuracy in the busy routine laboratory, yet small enough to qualify as a micro procedure for pediatric use, (3) there should be a minimum of reagents, with good stability, (4) accurate and reproducible results should be obtained on all types of sera, whether clear, hemolyzed, jaundiced, or lipemic, and (5) the method should be specific and rapid. Two possibilities were thought of to meet the above requirements: the determination of calcium by flame photometry, or some procedure using a chelating agent and a selected indicator in a medium which would make the determination specific for calcium. The introduction of flame photometry was once thought to be the answer to the problem, but its application for the analysis of calcium in biologic material leaves much to be desired. Most effective procedures use some method to isolate the calcium, either wet ashing (1,