STRONTIUM (II)-SELECTIVE ELECTRODE BASED ON A MACROCYCLIC LIGAND

Abstract

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) phosphate (TEP), dibutyl butylphosphonate (DBBP), and tributyl phosphate (TBP) as plasticizing solvent mediators was prepared and investigated as a Sr(II)-selective electrode. The best performance was observed with the membrane having the ligand-PVC-DBP-STB composition 1:4 : 1:1, which worked well over a wide concentration range (1.4 × 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 selectivity of Sr(II) ions over a large number of cations including Ca(II) and Ba(II). Anions such as Cl− and SO4 2 do not interfere and the electrode also works satisfactorily in partially water-alcohol medium. The sensor has been used as an indicator electrode in the potentiometric titration of Sr(II) with EDTA. The practical utility of the membrane sensor has also been observed in solutions contaminated with detergents i.e., cetyltrimethylammonium bromide and sodium dodecyl sulfate.