A flame photometric method for the determination of plasma magnesium after hydroxyquinoline precipitation.

The numerous methods for determining magnesium in biological fluids that have been reported in the past have varied from chemical to spectrochemical techniques. Among these various procedures have been included gravimetric, calorimetric, and titrimetric techniques. The gravimetric micromethod based on the precipitation of magnesium B-hydroxyquinoline in hot ammoniacal solution, first utilized by Hahn (1) in 1926, has been implemented by numerous calorimetric applications. The hydroxyquinoline has been determined calorimetrically in the method of Yoshimatsu (2) and of Eichholtz and Berg (3) by utilization of the Folin phenol reagent. A further calorimetric application of the hydroxyquinoline precipitation involving the formation of a specific green-blue color by the reaction of ferric ions with magnesium hydroxyquinoline has been described by Hoffman (4). He does not consider the possible complications encountered in hemolyzed serum samples. Independent of the hydroxyquinoline precipitation, some of the more recent calorimetric procedures have utilized the well known titan yellow reaction (5, 6). Essentially, titrimetric methods have involved bromination of magnesium hydroxyquinoline with bromate and eventual iodometric titration of the excess bromate. Greenberg and Mackey (7) have described such a procedure, introducing the Kirk-Schmidt micro filter (8) for collection of the precipitate. Further modifications of the bromination technique have been described by Velluz (9), Berg (lo), and Glomaud (11). The variety of methods described and the numerous modifications of each suggest a general dissatisfaction with them. The need for a sensitive accurate method of magnesium analysis for the determination of low concentrations in biological fluids has suggested the use of flame photometry described here. By this method, a series of twenty-four determinations of plasma magnesium may be completed in a period of 3 hours.