Potentiometric Membrane Electrode for Salicylate Based on an Organotin Complex with a Salicylal Schiff Base of Amino Acid

Abstract

A novel salicylate-selective electrode based on an organotin complex with a salicylal Schiff base of amino acid salicylaldehydeaminoacid-di-n-butyl-Sn(IV) [Sn(IV)-SAADB] as ionophore is described, which exhibits high selectivity for salicylate over many other common anions with an anti-Hofmeister selectivity sequence: Sal^- » PhCOO^-> SCN^- > ClO₄^- > I^- > NO₃^- > NO₂^- > Br^- > Cl^- > CH₃COO^-. The electrode, based on Sn(IV)-SAADB, with a 30.44 wt% PVC, a 65.45 wt% plasticizer (dioctyl phthalate, DOP), a 3.81 wt% ionophore and a 0.3 wt% anionic additive is linear in 6.0 × 10^-6 - 1.0 × 10^-1 mol l^-1 with a detection limit of 2.0 × 10^-6 mol l^-1 and a slope of 62.0 ± 1.2 mV/decade of salicylate concentration in a phosphate buffer solution of pH 5.5 at 25°C. The influence on the electrode performances by lipophilic charged additives was studied, and the possible response mechanism was investigated by UV spectra. The electrode was applied to medicine analysis and the result obtained has been satisfactory.