Theoretical and experimental approaches to the use of benzoyl carbamothioyl alanine as a new ionophore for development of various mercury selective electrodes

Abstract

Benzoyl carbamothioyl alanine (BCA) was prepared, characterized, and applied as an ionophore to fabricate three new mercury-selective potentiometric sensors. First, the molecular mechanic-based MMFF94 technique was used to determine the most stable BCA’s conformer and its isosteric complexes with some cations. The reaction’s Gibbs free energy results indicated the acceptable thermodynamic complexation reactivity of the ligand and Hg2+. The quantum theory of atoms in molecules revealed that the interaction of Hg2+ with oxygen and sulfur atoms corresponded to electrostatic nature and partial covalency, respectively. FTIR spectra indicated that the Hg2+ ion could coordinate with a BCA molecule through sulfur, oxygen, and nitrogen atoms. The theoretical thermodynamic parameters calculated in the solvent phase and the experimental selection pattern extracted from UV–visible spectroscopy showed excellent agreement. The morphology of the PVC membrane was studied using field emission-scanning electron microscopy and the presence of Hg2+ ions in the membrane matrix was confirmed by the analysis of EDX spectra. Overall, using the mentioned ligand, three different liquid membrane mercury selective electrodes were constructed: liquid internal electrolyte-ion selective electrode (LIE-ISE), coated wire-ISE (CW-ISE), and solid state-ISE (SS-ISE). Responses were Nernstian for all of the electrodes. The detection limit was improved for CW-ISE (7 × 10-6 M) and SS-ISE (7 × 10-9 M) compared to LIE-ISE (1 × 10-5 M). Also, the response time of LIE-ISE was approximately 15 s, while it was 5 s for both CW-ISE and SS-ISE. The sensors were applied as indicator electrodes in the potentiometric titration of Hg2+ with ethylenediaminetetraacetic acid.