A colorimetric method for the estimation of serum magnesium.

I955 The author wishes to express his sincere appreciation to Dr R. E. Hungate for an introduction to the fascinating cattle protozoa and for many stimulating discussions during the course of the experiments. The investigation was supported in part by funds for biological and medical research by the State of Washington, initiative measure number 171. In clinical work, where general electrolyte depletion occurs, there may be disturbances of serum magnesium which require correction. These deficiencies have been shown by Flink, Stutzman, Anderson, Konig & Frazer (1954) to occur sometimes in chronic alcoholics and in patients on continuous intravenous therapy. These authors reported neurological symptoms similar to those described in animals by Kruse, Orent & McCollum (1932) and by Greenberg & Tufts (1938). Evidence of change in the magnesium levels of the cerebrospinal fluid in human subjects was found by McCance & Watchorn (1932) in cases of chronic meningeal inflammation, but no symptoms were ascribed to this. Smith (1949) showed that a raised serum magnesium concentration in the dog caused a flaccid paralysis. The importance of magnesium is also evident in intermediary metabolism, since magnesium is needed as an enzyme activator in oxidative decarboxylation and is involved in adenosine triphosphate energy-release mechanisms (Baldwin, 1947). Interest in magnesium levels in clinical work is increasing and there is a need for a method of serum magnesium estimation suitable for a routine clinical laboratory. The earliest method for the estimation of magnesium was gravimetrically as magnesium am-monium phosphate (McCrudden, 1909), and in the following period many micro-methods applicable to serum were based on the estimation of phosphate in the precipitates by various procedures. Decoloriza-tion of ferric thiocyanate was used by Marriott & Howland (1917), and by Kramer & Tisdall (1921), who combined calcium and magnesium estimations by consecutive precipitation of calcium as oxalate, and magnesium as magnesium ammonium phosphate. Denis (1920) used a nephelometric method with strychnine molybdate. Upon the introduction of the colorimetric estimation of phosphate by Bell & Doisy (1920), this was applied to the magnesium ammonium phosphate precipitate by Denis (1922), Hammett & Adams (1922), and with modifications by Briggs (1922a, b, 1924). The colorimetric method of Fiske & Subbarow (1925) was subsequently used until Simonsen, Westover & Wertman (1947) introduced molybdivanadate for the estimation of phosphate. A different principle was used by Greenberg & Mackey (1932), in which calcium was removed and magnesium precipitated by 8-hydroxyquinoline, which was estimated volumetrically; …