Spectrophotometric determination of magnesium with eriochrome black T

The dependence of optical density of solution of complex compound of magnesium with eriochrome black T on wavelength of absorbing radiation has been studied. It has been shown that the maximum absorption of complex compound of magnesium with eriochrome black T is observed at a wavelength of 550-560 nm, while the maximum absorption of eriochrome black T solution is observed at wavelengths of 610-620 nm. It has been found that complex compound of magnesium with eriochrome black T significantly depends on ph of solution medium. The optimal ph of solution medium, at which the process of complex formation of magnesium with eriochrome black T occurs, has been revealed. The dependence of optical density on concentration of complex magnesium compound at a wavelength of maximum light absorption equal to 560 nm at ph = 10.0 - 10.5 has been determined. The proposed method has been used to determine the magnesium content in a number of mineral waters and samples of medical preparation 'Magnesium sulfate'. The obtained results of spectrophotometric studies of complex compound of magnesium with eriochrome black T have been compared with the results of complexometric titration of magnesium ions with complexone III. It has been found that the results of spectrophotometric studies are consistent with the results of titrimetric analysis. (author)