Ion-selective electrodes based on long-chain quaternary ammonium salts with enhanced steric accessibility, and their application for determination of hydrophilic double-charged inorganic anion

Abstract

The effect of long-chain quaternary ammonium salts’ exchange center steric accessibility and presence of a neutral anion carrier, 4-(trifluoroacetyl)benzoic acid heptyl ester, upon analytical characteristics of ion-selective electrodes reversible to molybdate, tungstate, sulfate, hydrogen phosphate, sulfite, carbonate and thiosulfate anions, has been studied. When the most sterically hindered quaternary ammonium salts, trinonyl octadecyl ammonium bromide, is replaced by one of the salts with the accessible exchange center, the selectivity is altered, the magnitude of the selectivity coefficient change being determined by the nature of the interfering ion. Thus, for carbonate- and sulfate-selective ISEs with hydrophobic thiocyanate ions as interference, the effect achieved is 6–8 orders of magnitude, while with nitrate ions as interference it is 3.4–5.7 orders, and for such hydrophilic interference ions as sulfate, chloride and oxalate, it is even less. Replacing trinonyl octadecyl ammonium bromide with a sterically accessible ammonium salt improves lower detection limit generally by 1–2 orders, while for sulfite and thiosulfate ISEs the effect is only 0.3–0.95 orders. The procedures for determination of sulfate, sulfite and carbonate ions in real objects (mineral water, dried fruits) have been proposed. They are simple, reasonably accurate, require only widely available equipment and can be recommended for use in chemical and food industries.