Spectrophotometric Determination of Magnesium, Calcium, Strontium and Barium Present in Pairs by Use of Tetramethylmurexide

A spectre-photometric method is described for the determination of magnesium* calcium, strontium and barium coexisting in binary mixtures. The method employs totramethyimurexide as an auxiliary ligand, and has been developed for pure two-component systems, such as are involved in investigations of cation-exchange equilibria on anionic polymers. The analysis is performed with calibration curves of the cp = f[Me(I), Me(II)], where q? is the ratio of two absorbances А г and A 2 measured at two suitable wavelengths, Xl and Я2. The wavelengths Ax and$A2 a r o chosen from the absorption spectra of solutions containing the separate metals Me(I) or Me(II). The absorption spectra of solutions containing the tetramethyl­ murexide complexes of Ca , Sr + or Ba 2 + ions are independent of the identity of the anions present in the system (Cl~, NOg and CH3COO~). The results show that two arbitrarily chosen elements of the alkaline earths can be determined with a good accuracy in the presence of each other over a large concentration range (0.001 —0.05 м). Calcium, strontium and barium can bo estimated with high accuracy in solutions containing a considerable excess of either magnesium or potassium, this exceeding the concentrations of the above alkaline-earth elements by factors of 100, 50 and 20, respectively. Calcium can also be estimated with barium or strontium present in a 30-fold or a 20-fold molar excess, respectively.