Simultaneous spectrophotometric determination of calcium and magnesium in mineral waters by means of multivariate partial least-squares regression

A method for simultaneous spectrophotometric determination of calcium and magnesium in mineral waters using multivariate calibration methods is proposed, The method is based on the development of the reaction between the analyses and Methylthymol Blue at pH 11, Two operational modes were used: static (spectral information) and flow injection (FI) (spectral and kinetic information), The selection of variables was studied. A series of synthetic solutions containing different concentrations of calcium and magnesium were used to check the prediction ability of the partial least-squares models, The method was applied to the analysis of mineral waters and the results were compared with those obtained by complexometry. No significant differences at the 95% confidence level were found, The proposed method is simple, accurate and reproducible, and it could be easily adapted as a portable (static mode) or automatic (FI) method.