Sulfate-selective electrodes based on hydrotalcites

An ion-selective electrode (ISE) for sulfate based on a dispersion of hydro talcite particles into a polymeric membrane using coated-wire (CW) configur ation is described. Membranes, based both on poly(vinyl chloride) (PVC) con taining different plasticizers and poly(dimethylsiioxane) (PDMS) were studi ed. The best performance in terms of slope (-29.6 +/- 0.8 mV per decade) an d response time ttl min) was displayed by the PDMS based membrane whereas t he linearity range (4.0x10(-5) to 4.0x10(-2) M) was practically the same fo r all the developed ISEs. The interference of hydrophobic inorganic anions was very low in comparison with the conventional ion-exchanger based electr odes, as shown by the selectivity coefficients determined by the matched po tential method (MPM). The selectivity was also good towards the most common univalent and divalent anions and improved in the presence of 2-[4-(2-Hydr oxyethyl)-1-piperarazinyl]et acid (HEPES). The potentiometric response was practically constant in the pH range 4-7. A successful application of sulfa te determination in commercial mineral waters, using direct potentiometry, is presented. (C) 2001 Elsevier Science B.V. All rights reserved.