Analytical Sciences

Response Characteristics of Anion-Selective PolymerMembraneElectrodes Based on Gallium(III), Indium(III) and Thallium(III)Porphyrins

Erich D. STEINLE, UlrichSCHALLER and Mark E. MEYERHOFF *

Department of Chemistry, TheUniversity of Michigan, Ann Arbor, MI 48109, USA

The potentiometric anion responses of ion-selective electrodes preparedwith polymeric membranes doped withgallium(III), indium(III) and thallium(III) metalloporphyrins are examined.These group XIII metals, when inserted intoeither octaethyl- or tetraphenyl-porphyrin derivatives and subsequentlyincorporated into plasticized poly(vinyl chloride)membranes, serve as anion ionophores with selectivity patterns that deviatesignificantly from the classical Hofmeisterseries for anions. The gallium(III) porphyrin-based electrodes exhibitsignificantly enhanced response toward fluoride,whereas the indium(III) and thallium(III) porphyrins display somepreference for chloride and also effectivelydiscriminate less hydrated anions such as perchlorate and nitrate. All ofthe metalloporphyrins investigated aredetermined to function via a charged carrier response mechanism.This mechanism is elucidated by correlating the effectof adding lipophilic ionic sites, either cationic (quaternary ammonium) oranionic (tetraphenylborate) salts, to theobserved anion selectivity and response patterns of themetalloporphyrin-based liquid /polymer membrane electrodes. (Keywords: Ion-selective electrode, anion sensor, gallium(III)porphyrin, indium(III) porphyrin, thallium(III) porphyrin,ionic sites)

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