Analytical Sciences

Potentiometric Responses of Expanded PorphyrinIncorporatedLiquid Membrane Electrodes toward a Series of Inorganicand Organic Anions

Xiao Ming LIN*1 , KayokoUMEZAWA*2 , KojiTOHDA*3 , HiroyukiFURUTA*4 ,q_Jonathan L. SESSLER*4 and YoshioUMEZAWA*3*

*1 Division of Environmental Conservation,Graduate School of Environmental Science, Hokkaido University,Sapporo 060, Japan
*2 Department of Chemistry, Faculty of Science, OchanomizuUniversity, Bunkyo, Tokyo 152, Japan
*3 Department of Chemistry, School of Science, The University ofTokyo, Hongo, Bunkyo, Tokyo 113, Japan
*4 Department of Chemistry and Biochemistry, University of Texas atAustin, Austin, Texas 78712, U S A

The potentiometric responses of liquid membrane electrodes based onexpanded porphyrins such as sapphyrin, rubyrinand triphenylrosarin, toward a series of organic carboxylates and inorganicanions were investigated. pH titration of theseexpanded porphyrin based electrodes with and without a guest anion in thesample solution showed that protonation ofthe expanded porphyrins at the surface of the electrode membrane is aprerequisite for accommodating the guest anionsand yielding their potential responses. The electrodes strongly respondedto benzoates, but rather less to inorganic anionsand saturated aliphatic organic carboxylates. The selectivity sequences forthe sapphyrin based electrode were found insome cases to deviate from the Hofmeister series; fluoride preference overchloride and bromide is particularly noted.Interesting responses were observed by the electrodes for discriminatinggeometrical isomers: hydrogenmaleate overhydrogenfumarate, and positional isomers: phthalate over iso- andterephthalate and trichloroacetate over di- and mono-chloroacetates. (Keywords: Liquid membrane electrode, expanded porphyrin, sapphyrin,rubyrin, triphenylrosarin, benzoate, positionalisomer, geometrical isomer, trichloroacetate, potentiometric response)

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