Chromium(III)-selective electrode based on a macrocyclic compound

Abstract

A poly(vinyl chloride)-based membrane of 3,10-c-meso-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11- tetraazacyclotetradecane diperchlorate with sodium tetraphenyl borate (STB) as an anion excluder and dibutyl phthalate (DBP), dibutyl butylphosphonate (DBBP), tris(2-ethylhexyl) phosphate (TEP) and tributyl phosphate (TBP) as plasticizing solvent mediators was prepared and investigated as a Cr(III)-selective electrode. The best performance was observed with the membrane having the ligand–PVC–DBP–STB composition 2:10:7:1, which worked well over a wide concentration range (1.77 × 10^–6–0.1 mol L^–1) with a Nernstian slope of 20 mV per decade of activity between pH 3.0 and 6.5. This electrode showed a fast response time of 15 s and was used over a period of 4 months with good reproducibility (s = 0.4 mV). The selectivity coefficients for mono-, di- and trivalent cations indicate excellent selectivity for Cr(III) ions over a large number of cations. Anions such as Cl^– and SO₄^2– do not interfere and the electrode also works satisfactorily in a partially non-aqueous medium. The sensor has been used as an indicator electrode in the potentiometric titration of Cr(III) 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. Above all, the membrane sensor has been used very successfully to analyse some food materials for the determination of Cr(III) ion.