A rapid atomic absorption method, using an air–acetylene flame, for the determination of calcium and magnesium is described. The sample is fused with a mixture of lithium and strontium borate and the ground fusion product is dissolved in dilute citric acid. Strontium and citric acid present in solution act as protecting agents and the interfering effect of the major constituents of silicate samples is thus eliminated. The use of organic acids (citric acid, EDTA) as solvents instead of inorganic acids (HCl, HNO3) has the advantage of increasing the absorption values of calcium and magnesium. The results of the analysis of several geochemical rock standards show good accuracy and reproducibility.
K. Govindaraju, "Use of Complexing Agents as Solvents for Atomic Absorption Determination of Calcium and Magnesium in Silicates," Appl. Spectrosc. 24, 81-85 (1970)