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

A poly(vinyl chloride)-based membrane of 3,10-c-meso-3,5,7,7,10,12,14,14-oc tamethyl-1,4,8,11-tetraazacyclotetradecane diperchlorate with sodium tetrap henyl borate (STB) as an anion excluder and dibutyl phthalate (DBP), dibuty l butylphosphonate (DBBP), tris(2-ethylhexyl) phosphate (TEP) and tributyl phosphate (TBP) as plasticizing solvent mediators was prepared and investig ated as a Cr(III)-selective electrode. The best performance was observed wi th the membrane having the ligand-PVC-DBP-STB composition 2 : 10 : 7 : 1, w hich worked well over a wide concentration range (1.77 x 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 selectivit y coefficients for mono-, di- and trivalent cations indicate excellent sele ctivity for Cr(III) ions over a large number of cations. Anions such as Cl- and SO42- do not interfere and the electrode also works satisfactorily in a partially non-aqueous medium. The sensor has been used as an indicator el ectrode in the potentiometric titration of Cr(III) with EDTA. The practical utility of the membrane sensor has also been observed in solutions contami nated with detergents i.e:, cetyltrimethylammonium bromide and sodium dodec yl sulfate. Above all, the membrane sensor has been used very successfully to analyse some food materials for the determination of Cr(III) ion.