Optimization of a flow injection differential potentiometric system with two identical electrodes for the determination of calcium ion in water with improved sensitivity

The optimization of a flow-injection analysis (FIA) system for the determination of calcium ions in water is described. The system was modified with 2 calcium ion-selective electrodes placed in series. Comparison with an equivalent conventional potentiometric FIA system revealed an increased sensitivity of 28-50 mV per decade (in the response range of 0.001-0.1 mol per litre) and better reproducibility (0.5-0.8 per cent compared with 1.7-1.9 per cent). The influence of ionic strength to the process is discussed.