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 ex panded porphyrins such as sapphyrin, rubyrin and triphenylrosarin, tow ard a series of organic carboxylates and inorganic anions were investi gated, pH titration of these expanded porphyrin based electrodes with and without a guest anion in the sample solution showed that protonati on of the expanded porphyrins at the surface of the electrode membrane is a prerequisite for accommodating the guest anions and yielding the ir 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 electr ode were found in some cases to deviate from the Hofmeister series; fl uoride preference over chloride and bromide is particularly noted. int eresting responses were observed by I:he electrodes for discriminating geometrical isomers: hydrogenmaleate over hydrogenfumarate, and posit ional isomers: phthalate over iso- and terephthalate and trichloroacet ate over di- and monochloroacetates.