Influence of anionic additive on Hg(2+) interference on Ag(+)-ISEs based on [2.2.2]p,p,p-cyclophane as neutral carrier.

The influence of the anionic additive on the Hg(2+) interference on Ag(+)-ion-selective electrodes (Ag(+)-ISEs) based on [2.2.2]p,p,p-cyclophane as pi-coordinating neutral carrier was studied by potentiometric measurements. The weakly coordinating carborane anion (7,8,9,10,11,12-hexabromocarborane, CB(11)H(6)Br(6)(-)) was compared with the commonly used tetrakis(4-chlorophenyl borate) (TpClPB(-)) as the anionic additive in plasticized PVC membrane-based Ag(+)-ISEs. The Hg(2+) interference was reduced by six orders of magnitude when replacing TpClPB(-) with CB(11)H(6)Br(6)(-) as the anionic additive, resulting in log K (Ag ,Hg )=-3.8+/-0.1 determined by the matched potential method (MPM). This indicates that weakly coordinating carboranes may be particularly useful as anionic additives in ISEs for soft cations.