Functionalized calixarene molecules 26, 28-dihydroxy-25, 27-dimethoxycalix[4]arene-11, 23-diphosphonic acid for Pb(II) and 25, 26, 27, 28-tetra-(2-dimethydithiocarbamoly-ethoxy)calix[4]arene for Hg(II) were tested as possible ionophores in Ion Selective Electrodes (ISEs) and successfully applied for the detection of heavy metal ions from environmental and industrial wastewaters. These membrane electrodes based on calixarene sensors are active in the pH range of 5.5-8.5. Calixarene sensors worked satisfactorily in aqueous as well as non-aqueous media up to 25% (v/v) non-aqueous content, and the life time of the sensors was observed to be five months. Potentiometric selectivity coefficients as determined by Match Potential Method (MPM) indicate excellent selectivity for Pb²⁺ and Hg²⁺ ions. The sensors could be used successfully in the estimation of lead and mercury in electrochemical battery wastes and also as indicator electrodes in potentiometric titration.

Determination of the heavy metals becomes one of the basic requirements in many chemical investigations nowadays. Toxicological and physiological investigations of heavy metals are crucial studies related to environmental aspects. The common methods applied for the determination of heavy metals are separation of the species by chromatography, followed by detection and determination of the element with a specific detector such as atomic absorption spectrometry or mass spectrometry (Berma, 1980; and Klassen et al., 1986). These methods are rather expensive and time-consuming. Thus, electroanalytical methods are much more effective in terms of species-selective detection than other reported methods. The basic principle of potentiometry with ion-selective electrodes is well suited to separation studies because of its selective response to free ions in aqueous solutions.

Based on the recent advance of host-guest chemistry, polymeric membrane ISEs for heavy metal ions have been extensively developed by the use of crown ether and related calixarene hosts as well as acyclic ligands (Ghidini et al., 1990; Asfari et al., 1994; Hill et al., 1994; O'Connor et al., 1994; Asfari et al., 1995; and O'Connor et al., 1996). In this paper, two functionalized calixarene molecules, viz., 26, 28-dihydroxy-25, 27-dimethoxycalix[4]arene-11, 23-diphosphonic acid (I) and 25, 26, 27, 28-tetra- (2-dimethydithiocarbamoly-ethoxy)-calix[4]arene (II) have been used as neutral ionophores in Poly(Vinyl Chloride) (PVC)-based Ion Selective Electrodes (ISEs) for lead(II) and mercury(II) ions, respectively.

All reagents used were of the commercially available analytical grade. Double distilled water was used for the preparation of solution of metal salts of different combinations by diluting stock standard solutions (0.1 M). High molecular weight PVC , tetrahydrofuran (THF) and dibutyl phthalate (DBP) were purchased from Sigma Aldrich. While metal salts in the form of nitrate or chloride were obtained from Merck. The functionalized calixarene molecules (I) and (II), as an ionophore, were prepared and purified as described previously (Yordanov et al., 1996; and Plutnar et al., 2002).

Chemistry Journal, Calixarene Ionophores, Heavy Metal Detections, Ion Selective Electrodes, Ises, Electroanalytical Methods, Mass Spectrometry, Physiological Investigations, Calixarene Molecules, Potentiometric Titrations, Potentiometric Method, Matched Potential Methods, Non-Aqueous Systems, Membrane Electrodes.