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

Resumo

A film polyvinyl chloride sulfate-selective electrode based on the sterically accessible higher quaternary ammonium salt, 3,4,5-tris(dodecyloxy)benzyl(oxyethyl)3trimethylammonium 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 × 10⁻⁷ 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⁻, C₂O₄⁻, Br⁻, and NO₃⁻ions. The interference of carbonate ions was eliminated by maintaining pH at 3.2 ± 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.