Thiocyanate-selective PVC membrane electrodes based on Mn(II) complex of N,N′-bis-(4-phenylazosalicylidene) o-phenylene diamine as a neutral carrier

A series of transition metal chelates of N,N '-bis-(4-phenylazosalicylidene) o-phenylene diamine (H2L) were synthesized and their anion response characteristics were investigated. The results show that the behavior of the electrode is considerably influenced by the properties of the central metals. A novel electrode prepared with the Mn(II) chelate exhibited a linear response towards thiocyanate over the concentration range of 0.1-7.02 x 10(-6) M in phosphate buffer solutions of pH 5.38 with a slope of -57.3 mV per decade, the electrode demonstrated an anti-Hofmeister selectivity behavior; the selectivity sequence observed was: thiocyanate > iodide > salicylate > benzoate > perchlorate > nitrite > bromide > acetate > nitrate > chloride. Electrodes based on the Co(II) chelate demonstrated a preferential response to iodide ion, Electrodes based on the Hg(II) and NI(II) chelates had weak anion response characteristics. The response mechanism was also investigated by use of impedance and spectroscopic techniques and the influence on the electrode performances by lipophilic charged additives. The electrodes were applied to the determination of thiocyanate in wastewater with satisfactory results. (C) 1999 Elsevier Science Ltd. All rights reserved.