Nickel(II)-selective sensors based on heterogeneous membranes of macrocyclic compounds

Membranes of 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene diperchlorate (I) and 3,5,7,7,10,12, 14,14-octamethyl-1,4,8, 11-tetraazacyclotetradeca-4, 11-diene diperchlorate (II) in PVC and polystyrene binders have been investigated as Ni2+-selective sensors. The PVC membranes containing macrocycles, di-n-butylphthalate and dioctylphthalate as plasticizing solvent mediators and sodium tetraphenylborate as an anion excluder show near-Nernstian response in the concentration range approximate to 10(-5)-10(-1) mol l(-1), while polystyrene-based membranes exhibit linearity in the concentration range approximate to 10(-6)-10(-1) mol l(-1). These membranes have response times as fast as 15 g and can be used over a period of six months. The electrodes work in the pH range 1.7-5.4 and also perform well in alcohol-water mixtures with alcoholic content up to 50%. The selectivity coefficient values reveal that the electrodes respond to Ni2+ ions selectively over a large number of cations. The membrane has also been used as an indicator electrode for the determination of the end point in the potentiometric titration of Ni2+ against oxine.