Flame Photometric Determination of Magnesium in Biological Samples

(Introduction) Mineral metabolism in human subjects is one aspect of the research in progress in the Nutrition Department at the University of Tennessee. When a study of magnesium metabolism was initiated a colorimetric method was sought form magnesium determinations in samples collected in the metabolic balance studies. A thiazole yellow colorimetric procedure, developed for analysis of plant tissue, was modified for analysis of ash solutions of food, feces, and urine. The method has proved thoroughly satisfactory and is fairly rapid. However, because of the large number of samples to be analyzed, use of a considerably faster flame photometric analysis seemed desirable if conditions suitable for magnesium determination in the biological materials could be established. Other ions present in the ash from food, feces, and urine interfere with magnesium analysis by the flame photometric method. The purpose of the work reported in this paper was to investigate procedures available for elimination of interference by sulfate, phosphate, calcium, sodium, and potassium in an attempt to find conditions which would permit satisfactory magnesium determinations in the types of materials to be analyzed. Reproducibility of analyses made at two different sample concentrations and in different series of determinations, recovery of magnesium added to solutions of ash, and agreement of results with those obtained by colorimetric analysis of the same samples were criteria for evaluation of procedures