Selectivity of solid-contact Ag potentiometric sensors based on thiacalix[4]arene derivatives

Potentiometric sensors based on glassy carbon electrode covered with polyaniline and thiacalix[4]arenes containing amidopyridine, morpholide, pyrrolidide and hydrazide functional groups in cone, partial cone and 1,3-alternate conformations have been developed and applied for determination of Ag+ ions in the range from 1.0 × 10−2 to 4.0 × 10−7 M and limits of detection from 1 × 10−7 to 3.5 × 10−8 M. The sensitivity of Ag+ detection decreases in the following range of thiacalix[4]arene substituents: morpholide > pyrrolidide > amidopyridine > hydrazide. Potentiometric selectivity coefficients predominantly showed binding of Ag+, Hg(II) and Fe(III) ions over other transient and alkali metals. The influence of functional groups and conformation of receptor on the selectivity of the sensor response was investigated. As shown, selectivity and sensitivity of Ag+ determination depends on the steric accessibility of the binding site and flexibility of the receptor structure. For Fe(III) ions, changes of the sensor potential are also determined by their implementation in redox reactions of polyaniline.