NICKEL(II)-SELECTIVE SENSORS BASED ON HETEROGENEOUS MEMBRANES OF MACROCYCLIC-COMPOUNDS

Membranes of amethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene diperc hlorate (I) and 3,5,7,7,10,12, 14,14-octamethyl-1,4,8, 11-tetraazacycl otetradeca-4, 11-diene diperchlorate (II) in PVC and polystyrene binde rs have been investigated as Ni2+-selective sensors. The PVC membranes containing macrocycles, di-n-butylphthalate and dioctylphthalate as p lasticizing solvent mediators and sodium tetraphenylborate as an anion excluder show near-Nernstian response in the concentration range appr oximate 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 p H range 1.7-5.4 and also perform well in alcohol-water mixtures with a lcoholic content up to 50%. The selectivity coefficient values reveal that the electrodes respond to Ni2+ ions selectively over a large numb er of cations. The membrane has also been used as an indicator electro de for the determination of the end point in the potentiometric titrat ion of Ni2+ against oxine.