Effect of varying quaternary ammonium salt concentration on the potentiometric properties of some trifluoroacetophenone derivative‐based solvent‐polymeric membranes

Potentiometric properties of carbonate‐selective membranes based on some trifluroacetophenone derivatives [e.g., trifluoroacetyl‐ p ‐decylbenzene (TFADB), 1,7‐bis(4′‐trifluoro‐acetophenyl)‐4‐decyl‐1,7‐dioxo‐2,6‐dioxy‐heptane (compound I) and 1,2‐bis(4‐trifluoroacetylbenzoyloxymethyl)‐benzene (compound II)] with varying concentration of tridedecylmethyl ammonium chloride (TDMACl) have been examined. It was observed that both TFADB‐ and compound‐II‐based membranes with about 50 mol % TDMACl (relative to the carrier) exhibit the maximum selectivity for carbonate. On the other hand, the compound‐I‐based membranes with about 50 mol % TDMACl showed the greatest discrimination of lipophilic anions (ClO 4 − , salicylate, SCN 3 − ) including NO   3 − , but those with about 80 mol % against Cl − and CH 3 COO − . These results conform well to the theoretical model developed by Simon et al. if we assume trifluroacetophenone derivatives form 2:1 and/or 3:1 complexes with the anions in the plasticized PVC‐based membranes. Molecular mechanics calculations indicated that bis‐trifluroacetophenones may not form 1:1 complex with the carbonate ion because of a large steric hindrance between the two bulky adjacent chains.