Unsymmetrical Tetradentate Schiff Bases Copper (II) Complex as Neutral Carrier for Thiocyanate‐Selective Electrode

Abstract

Three kinds of transition metal chelates of unsymmetrical tetradentate Schiff base, o‐hydroxybenzophenone‐1,2‐diaminobenzene‐pyrrole‐2‐carbaldehyde(H₂L), were synthesized to prepare anion‐selective electrodes and their anion response characteristics were investigated. The results show that the performances of the electrodes are considerably influenced by the nature of the central metals. The proposed electrode with the Cu(II)‐chelate and cationic additive demonstrated an anti‐Hofmeister selectivity sequence with a good selectivity towards thiocyanate in the following order: Thiocyanate>iodide>salicylate>perchlorate>bromide>nitrite>chloride>acetate>fluoride>nitrate>sulfite>sulfate. The electrode had an excellent linear response to thiocyanate from 3.4×10⁻⁷ to 1.0×10⁻¹ M in phosphate buffer solution at pH 5.0 with a slope of −58.7 mV per decade, a detection limit of 1.6×10⁻⁷ M, and a fast response time within 5 s over the entire concentration series. Spectroscopic techniques and AC impedance were used to investigate the response mechanism to thiocyanate of the membrane doped with Cu(II)‐chelate. The preliminary application of the electrode for determination of thiocyanate in wastewater and urine samples is reported.

Keywords:

• Unsymmetrical Schiff base
• thiocyanate‐selective electrodes
• neutral carrier
• o‐hydroxybenzophenone‐12‐diaminobenzene‐pyrrole‐2‐carbaldehyde

The support of the National Natural Science Foundation of China (20675064), the Chinese Education Ministry Foundation for the excellent young teachers, and the Natural Science Foundation of Chongqing City, China is gratefully acknowledged.