Effect of the Nature of a Quaternary Ammonium Salt and the Addition of a Neutral Carrier on Analytical Characteristics of Sulfate-Selective Electrodes

A film polyvinyl chloride sulfate-selective electrode based on the sterically accessible higher quaternary ammonium salt, 3,4,5-tris(dodecyloxy)benzyl[(oxyethyl).sub.3]trimethylammonium chloride, using 1-bromonapthalene as a plasticizer and heptyl p-trifluoroacetylbenzoate as a solvating agent was developed. The limit of detection of the electrode was 6.7 x [10.sup.-7] M, lifetime was 1 month, and the slope of the electrode function was 27 mV/decade. The electrode is selective in the presence of interfering [Cl.sup.-], [C.sub.2][O.sup.2-.sub.4], Br-, and N[O.sup.-.sub.3] ions. The interference of carbonate ions was eliminated by maintaining pH at 3.2 [+ or -] 0.1. Based on IR spectroscopic and potentiometric studies, it is most likely that the solvation of sulfate ions with heptyl p-trifluoroacetylbenzoate occurs through interaction with the trifluoroacetyl carbonyl carbon atom rather than with hydroxyl groups of the hydrate form. Keywords: sulfate-selective electrode, sterically accessible quaternary ammonium salt, heptyl p-trifluoroacetylbenzoate
Sulfates are contained in sea, mineral, and industrial waste waters, food products, and atmospheric precipitations and used in the chemical and pharmaceutical industry among others. Sulfate ions are determined by [...]