Potentiometric Responses of Expanded Porphyrin Incorporated Liquid Membrane Electrodes toward a Series of Inorganic and Organic Anions

The potentiometric responses of liquid membrane electrodes based on expanded porphyrins such as sapphyrin, rubyrin and triphenylrosarin, loward a series of organic carboxylates and inorganic anions were investigated. pH titration of these expanded porphyrin based electrodes with and without a guest anion in the sample solution showed that protonation of the expanded porphyrins at the surface of the electrode membrane is a prerequisite for accommodating the guest anions and yielding their potential responses. The electrodes strongly responded to benzoates, but rather less to inorganic anions and saturated aliphatic organic carboxylates. The selectivity sequences for the sapphyrin based electrode were found in some cases to deviate from the Hofmeister series; fluoride preference over chloride and bromide is particularly noted. Interesting responses were observed by the electrodes for discriminating geometrical isomers: hydrogenmaleate over hydrogenfumarate, and positional isomers: phthalate over iso- and terephthalate and trichloroacetate over di- and monochloroacetates.