A ditopic calix[4]pyrrole amide derivative: highlighting the importance of fundamental studies and the use of NaPh4B as additive in the design and applications of mercury(II) ion selective electrodes

The use of calixpyrroles as cation monitoring systems is very limited. The importance of fundamental studies for providing the basis for the selection of an appropriate ionophore for use in the design of ion selective electrodes cannot be overemphasised. Thus a new ditopic receptor, namely meso-tetramethyltetrakis-(4N,N-diethylacetamide) phenoxymethyl]calix[4]pyrrole (CPA), bearing cation and anion recognition sites has been synthesized and characterized using NMR measurements in acetonitrile. This new receptor interacts with Ca(II), Sr(II), Ba(II), Pb(II) and Cd(II) perchlorate salts and Hg(II) (nitrate as counter-ion). Among the cations tested, 1 : 1: complexes were found between CPA and the above mentioned cations except Hg(II) for which a 1 : 2 (ligand : metal cation) complex is found. These fundamental studies provided the basis for the design of a Hg(II) ion selective electrode (ISE). A detailed investigation on possible interactions between the analyte and the individual components of the membrane in solution as well as in membranes prepared in the absence of the receptor, revealed that NaPh4B, an additive frequently used in the preparation of mercury ion selective membranes, interacts with Hg(II). The implications of these findings on previously reported (Hg(II) ISE) are discussed. The optimum working conditions of the new electrode on its potentiometric response were established. Selectivity coefficients of Hg(II) relative to other cations were calculated. The advantages of this electrode relative to others reported in the literature are discussed. Analytical applications include its use as an indicator electrode as well as for the quantitative determination of this cation in an amalgam.