Potentiometric Discrimination of Fluoro- And Chlorophenol Isomers Based on the Host Functionality of Calix[4]pyrrole at Liquid Membrane Surfaces

Abstract

This work presents a study on the generation of an ''anionic'' potentiometric response of a liquid polymeric membrane based on calix[4]pyrrole towards neutral chloro-and fluorophenol isomers. The results show that a calix[4]pyrrole membrane is able to recognize chloro and fluoro derivatives of phenols, and discriminate between ortho-, meta-, and para-isomers of chlorophenol. The mechanism of molecular ANALYTICAL LETTERS recognition relies on the formation of a supramolecular complex between a phenolic guest and the calix[4]pyrrole host occurring at the organic/aqueous interface, which leads to a change of charge separation. The sensitivity and selectivity of the sensor studied depend on the acidity and lipophilicity of the phenolic analytes. The selected matrix effect on the potentiometric measurements has been checked.

Interface HostGuest Interaction Between Calix[4]pyrrole and Neutral Derivatives of Phenol as the Base for Their Potentiometric Discrimination

“…One at 305 nm, is characteristic for para-nitrophenol, and a new one, at 285 nm, is connected with the para-nitrophenol À calix [4]pyrrole 1 complex. The negligible response of the calix [4]pyrrole-membranes towards the ortho-isomer of nitro-and chlorophenol [10], which have intramolecular hydrogen bonds, also supports this assumption.…”

“…Ortho-nitrophenol and ortho-chlorophenol [10] showed a very weak potential response in comparison to the paraisomers. The acidity of ortho-and para-nitrophenols is similar (pK a 7.21 and 7.16, respectively), whereas the acidity of ortho-chlorophenol is higher than the acidity of parachlorophenol (pK a 8.11 and 9.20, respectively).…”

“…The exceptions are ortho-nitrophenol and ortho-chlorophenol [10]. These compounds caused very weak potential response even though their acidity is rather high in this group.…”

“…Membranes modified with calix [4]pyrroles are able to generate a very sensitive and selective potentiometric response towards neutral phenols derivatives [9,10].…”

Polymeric Liquid Membrane Electrodes Incorporated with Undecylcalix[4]-Resorcinarene for Screening of Neutral Forms of Diaminobenzene Isomers

“…The results reported there showed that not only membrane modified with quaternary ammonium salts and lipophilic polyamines, but also those based on calix [4]pyrrole [13][14][15][16], corrole [17], and amino-calix [4] resorcinarenes [18] are able to generate anionic potentiometric responses after stimulation by undissociated form of phenol derivatives.…”