**1. Introduction**

Recently one could observe a continuous increase of scientific interest in host-guest chemistry, and more specifically in the intermolecular recognition processes occurring at liquid-liquid interface [1-3, 7, 8]. The fundamental chemical processes occurring in liquid membrane of potentiometric sensor are guest- induced selective changes in the charge separation across the interface between the liquid membrane and aqueous sample solution. The organic/aqueous interface, often named as "the third phase", possesses unique properties, which are very different from the properties of the bulk phases. In this particular place, many of biological processes of intermolecular recognition occur, demonstrating extremely high selectivity and sensitivity. Numerous instrumental methods were applied for study this phenomenon. Electrochemical one have a significant share in this research.

Potentiometry with using of ion selective electrodes (ISEs) is one of the most popular techni‐ ques enable to observe the recognition processes between the ligand and cationic or anionic species occurring in the liquid/liquid interface. The mechanism of potentiometric signal generation relies on the charge separation between two phases, which is the result of a perm selective transfer of analyte ions from the aqueous to the organic phases at the liquid /liquid interface with high sensitivity and selectivity [9, 10]. This type of sensors have some outstand‐ ing advantages including simple design and operation, wide linear dynamic range, relatively fast response and rational selectivity and because of these parameters there are particularly interesting from the perspective of the supramolecular chemist. The potentiometric sensors could be applied as a tool for observation of molecular recognition processes at the border of two phases.

In pioneering paper written by Umezawa and co-workers the possibilities of potentiometric signals generation of polymeric membrane modified with permanently charged ligand such

© 2013 Radecki and Radecka; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Radecki and Radecka; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

as quaternary ammonium salts [4] and lipophilic polyamines [5, 6] after their stimulation with uncharged phenol derivatives were described the first time. According to authors the mech‐ anism of signal generation by membrane modified with quaternary ammonium salts consist of two processes.

First is the complexation of extracted ArOH and Q+ X leading to a net movement of anionic species (X- ) from the aqueous to the membrane phase. In second step there is proton dissoci‐ ation of complexed ArOH and simultaneous ejection of HX to aqueous phase, involving a net movement of cationic species (H+ ) from membrane to the aqueous phase [4].

Being inspired by this paper, we have done systematic study on potentiometric signals generated by membranes modified with electrically neutral host molecules and stimulated with uncharged guest molecules [11-25].

As a receptors (host) molecules for recognition of uncharged phenol derivatives, corroles, calix[4]pyrroles, calix[4]phyrins and metalloporphyrines we have applied. Whereas, for recognition of unprotonated aniline derivatives we have used: *p*-*tert*-butylthiacalix[4]arene (BTC[4]ene), tetrabromodialkoxythiacalix[4]arene (BATC[4]ene), tetra-undecylcalix[4]resor‐ cinarene (UDC[4]Rene), tetra-undecyl-tetra-*p*-nitrophenylazocalix[4]resorcinarene (UDAC[4]Rene), tetra-undecyl-tetra-hydroxycalix[4]resorcinarene (UDHC[4]Rene), tetraundecyl-tetra-bromocalix[4]resorcinarene (UDBC[4]Rene.
