The determination of serum magnesium by the molybdivanadate method for phosphate.

During the past decade there has been an increasing interest shown in the study of electrolyte balance. Magnesium, however, has played a minor r81e in these studies. There are perhaps two reasons for this; first, that serum magnesium levels remain fairly constant and, second, that magnesium determinations require special technique and equipment and are time-consuming procedures as well. There have been three major methods used for the determination of serum magnesium, the molybdenum blue, titan yellow, and hydroxyquinoline methods. Molybdenum Blue-Briggs (1) and Denis (2) simultaneously reported methods for the determination of serum magnesium based upon the precipitation of magnesium as magnesium ammonium phosphate, with subsequent estimation of the phosphate by the molybdenum blue method. The above procedures were employed in this laboratory with the modifications for phosphate determination used by Kuttner and Cohen (3) and Youngburg and Youngburg (4). The molybdenum blue method was abandoned chiefly because of instability of the color. A more complete discussion of this is given in a publication (5) in which the molybdivanadate method, as outlined by Kitson and Mellon (6), was used for the estimation of serum phosphate. Titan Yellou+The titan yellow method is based on the fact that magnesium imparts a pink color to an alkaline solution of the dye (7). The clinical method of Him&elder and Serles (8) and the modification of Haury (9) were used, but difficulty was encountered because of the mixture of pink and yellow colors. In addition, the color wss markedly affected by variations in pH and salt concentration. Hydrmyquinoline-Hahn (10) and Berg (11) introduced the use of 8-hydroxyquinoline for the determination of magnesium. The method was further modified by the bromination technique of Bomskov (12), Greenberg and Mackey (13), and Velluz (14). Hoffman (15) discarded the bromination method in favor of a calorimetric procedure in which hydroxyquinoline combines with ferric ions in weak hydrochloric acid