Flame Photometric Determination of Electrolytes in Tissue and of Calcium in Serum

The convenience and accuracy of flame photometric methods for the determination of sodium and potassium in body tissues and fluids suggest the desirability of determining other cations such as calcium and magnesium in the same sample.While reliable procedures for the determination of sodium and potassium have been developed (1, 2), there are apparently no satisfactory flame spectrophotometric methods available for the determination of calcium and magnesium in tissue.In the following, one flame photometric method is described which permits the simultaneous determination of calcium, magnesium, sodium, and potassium in tissue, and another method is described for determining calcium in blood serum.EXPERIMENTAL By employing flame spectrophotometric methods, phosphates have been found to depress calcium luminosity (3-5).It has been observed here that phosphates also decrease the luminosity of magnesium.It is, therefore, necessary to remove phosphates in order to obtain reliable analytical data for either calcium or magnesium.Fields et al. (3) eliminated this interference by coprecipitating the phosphate with iron hydroxide.However, this method may entail some losses of calcium and magnesium and is rather time-consuming.Several investigators (5, 6) have adjusted the phosphate concentration in the standards to that of the unknowns.This is not too satisfactory since it is often difficult to predict the phosphate concentration of the sample to be analyzed.In the procedure described here, phosphate interference is eliminated by passing the solution to be analyzed through a cation exchange column.The anions pass through while the cations are exchanged and are then eluted with 6 N HCl.Method Instrument-A Beckman model DU spectrophotometer with a model No. 9200 flame attachment was used.