Strontium (II) - Selective electrode based on a macrocyclic ligand

A poly(vinyl chloride)-based membrane of 2,9-dimethyl-4, 11-diphenyl-1,5,8, 12-tetraazacyclotetradeca-1,4,8,11-tetraene with sodium tetraphenylborate ( STB) as an anion excluder and dibutyl phthalate (DBP), tris(2-ethylhexyl) p hosphate (TEP), dibutyl butylphosphonate (DBBP), and tributyl phosphate (TB P) as plasticizing solvent mediators was prepared and investigated as a Sr( II)-selective electrode. The best performance was observed with the membran e having the ligand-PVC-DBP-STB composition 1: 4: 1: 1, which worked well o ver a wide concentration range (1.4 x 10(-6)-0.1 mol L-1) with a Nernstian slope of 28.6 mV per decade of concentration between pH 4.0 and 10.0. This electrode showed a fast response time of 12 s and was used over a period of 100 d with good reproducibility (s = 0.3 mV). The selectivity coefficients for monovalent, divalent and trivalent cations indicate excellent selectiv ity of Sr(II) ions over a large number of cations including Ca(II) and Ba(I I). Anions such as Cl- and SO42- do not interfere and the electrode also wo rks satisfactorily in partially water-alcohol medium. The sensor has been u sed as an indicator electrode in the potentiometric titration of Sr(II) wit h EDTA. The practical utility of the membrane sensor has also been observed in solutions contaminated with detergents i.e., cetyltrimethylammonium bro mide and sodium dodecyl sulfate.