A chemometric study of the simultaneous determination of calcium and magnesium in natural waters

A method for the simultaneous spectrophotometric determination of calcium a nd magnesium in mineral waters with an FIA system is tested. The method is based on the reaction between the analytes and arsenazo(III) at pH 8.5. The calculations of the amounts of both analytes in the samples are carried ou t with the H-point standard addition method (HPSAM) for ternary mixtures, a nd with a partial least squares (PLS) model after a proper variable selecti on. The results obtained for the determination of calcium were comparable u sing both methods. The employment of the HPSAM brings to our attention the influence of the calcium concentration in the sample to the development of the reaction between magnesium and arsenazo(III). HPSAM also permits to est imate the concentration of magnesium in the samples. (C) 1999 Elsevier Scie nce B.V. All rights reserved.