Sulfate-selective electrodes based on hydrotalcites

An ion-selective electrode (ISE) for sulfate based on a dispersion of hydrotalcite particles into a polymeric membrane using coated-wire (CW) configuration is described. Membranes, based both on poly(vinyl chloride) (PVC) containing different plasticizers and poly (dimethylsiloxane) (PDMS) were studied. The best performance in terms of slope (-29.6± 0.8mV per decade) and response time (<1min) was displayed by the PDMS based membrane whereas the linearity range (4.0×10-5 to 4.0×10-2M) was practically the same for all the developed ISEs. The interference of hydrophobic inorganic anions was very low in comparison with the conventional ion-exchanger based electrodes, as shown by the selectivity coefficients determined by the matched potential method (MPM). The selectivity was also good towards the most common univalent and divalent anions and improved in the presence of 2-[4-(2-Hydroxyethyl)-1-piperarazinyl]ethanesulfonic acid (HEPES). The potentiometric response was practically constant in the pH range 4-7. A successful application of sulfate determination in commercial mineral waters, using direct potentiometry, is presented.