NITRATE ION-SELECTIVE COATED-WIRE ELECTRODE BASED ON TETRAOCTADECYLAMMONIUM NITRATE IN SOLID SOLVENTS AND THE EFFECT OF ADDITIVES ON ITS SELECTIVITY

A nitrate ion-selective coated-wire electrode was prepared by dipping a graphite tip into a molten mixture of stearyl alcohol base and tetraoctadecylammonium nitrate ion exchanger. The selectivity coefficients for various inorganic and organic interferents were measured for membranes with and without an additive. The electrode without an additive showed a unique anion-selectivity pattern, i.e., the interference from perchlorate, organic carboxylates and sulfonates significantly decreased, while o-nitrophenyl octyl ether changed the selectivity pattern into the conventional one that conformed to the Hofmeister series. Other nitrophenoxy compounds also changed the selectivity pattern; however, the change was found to be time dependent.