AUTOMATIC SIMULTANEOUS DETERMINATION OF CA AND MG IN NATURAL-WATERS WITH NO INTERFERENCE SEPARATION

In this study a methodology is reported for the automatic, simultaneou s determination of Ca and Mg in natural waters which is not affected b y the presence of species that may interfere with other methods. A flo w system based on the sinusoidal injection analysis (SIA) methodology with diode array spectrophotometric detection of the complex formed by both analytes with the Arsenazo III has been used. The technique of m ultivariate calibration used, PLS1, enables Ca to be determined in the concentration range 45-85 mg l-1 and Mg to be determined in the range 2-70 mg l-1, with no need for the samples to be previously diluted. T he accuracy of the method has been tested by comparing the results obt ained with the standard atomic absorption spectrometry method. With an analysis speed of 20-30 samples per hour, the RMSE in terms of standa rd deviation of the original variables was 6.1 for Mg and 6.4 for Ca.