The determination of magnesium in biological materials by flame photometry.

A method is described for the measurement of magnesium in biological materials and has been applied to the Unicam flame spectrophotometer SP 900. Samples were diluted in 10 mM strontium ethylenedinitrolo tetraacetate (EDTASr), 10 mM potassium carbonate, giving final magnesium concentrations of about 0.1 to 0.2 mM. The EDTASr almost eliminated the depression of magnesium emission by interfering anions. The potassium carbonate slightly depressed both magnesium emission and flame background, which were then virtually unaffected by further addition of cations. Spectral interference by sodium was controlled by including 14 mM sodium chloride in the plasma standards and making small corrections (usually under 2%) on the basis of the plasma sodium level. The urine standards contained no sodium, but a small correction (usually about 2%) was made on the basis of the urine sodium level. There was insufficient sodium in faeces to cause spectral interference. Using the diluent described, added magnesium was satisfactorily recovered from plasma deproteinized with perchloric acid, urine, and faeces. When different volumes of identical samples of plasma and urine were analysed, the magnesium found was proportional to the volume of sample diluted. The plasma magnesium levels reported for a small group of healthy people were similar to those found by previous workers.