OPTIMIZATION OF A FLOW-INJECTION DIFFERENTIAL POTENTIOMETRIC SYSTEM WITH 2 IDENTICAL ELECTRODES FOR THE DETERMINATION OF CALCIUM-ION IN WATER WITH IMPROVED SENSITIVITY

An experimental optimization by the modified simplex method of a flow injection analysis (FIA) system for the differential potentiometric de termination of calcium ion in mater is reported, The performances of t he optimized system and of an equivalent conventional potentiometric F IA system are compared, The most important features of the proposed sy stem are a substantial increase in sensitivity (from about 28 to shout 50 mV per decade) in the linear response range (10(-4) - 10(-2) mol l (-1) in both cases) and better repeatability (0.5 and 0.8% versus 1.7 and 1.9%, respectively, at 1 x 10(-3) and 6.2 x 10(-4) mol l(-1) calci um ion), The influence of the ionic strength is discussed, showing tha t it significantly affects the accuracy of the results. The relative a ccuracy of the differential system was demonstrated try the determinat ion of the calcium content of drinking Waters in parallel with an ASTM certified method.