New cadmium(II)-selective electrode based on a tetraazacyclohexadeca macrocyclic ionophore.

A poly(vinyl chloride)-based membrane of 3,4:11,12-dibenzo-1,6,9,14-tetraazacyclohexadecane with sodium tetraphenyl borate (NaTPB) as an anion excluder and dibutylphthalate (DBP), dibutyl(butyl)phosphonate (DBBP), tris(2-ethylhexyl)phosphate (TEHP) and tributyl phosphate (TBP) as a plasticizing solvent mediator was prepared and investigated as a Cd2+-selective electrode. The best performance was observed with the membrane having a ligand-PVC-DBP-NaTPB composition of 2:25:60:1, which worked well over a wide concentration range (1.6 x 10(-6) - 1.0 x 10(-1) M) with a Nernstian slope of 29.5 mV per decade of activity between pH 2.0 - 6.0. This electrode showed a fast response time of 13 s and was used over a period of 4 months with good reproducibility (S = 0.4 mV). The selectivity coefficient for mono-, di- and trivalent cations indicated excellent selectivity for Cd2+ ions over a large number of cations. Anions such as NO3- and SO4(2-) , did not interfere. The membrane sensor has been successfully used to determine Cd2+ in real samples.