A new macrocyclic polystyrene-based sensor for chromium (III) ions

Abstract.

A new tetradentate dihydrogen perchlorate macrocyclic ligand (2,4,9,11-tetraphenyl-1,5,8,12-tetraazacyclotetradeca-1,4,8,11-tetraene dihydrogen perchlorate) was prepared and characterised. The macrocycle behaves as a selective chelating ion-exchanger for some metal ions. The polystyrene-based membrane electrode is found to exhibit quite promising selectivity for Cr³⁺ ions. It can be used to estimate chromium concentrations in the range 3.16×10^–6–1.00×10^–1 M with a near-Nernstian slope of 17.5 mV per decade of concentration between pH 3.0 to 6.5. The electrode is found to possess a fast response time of 15 s and was used over a period of three months with good reproducibility (s = ± 0.3 mV). The selectivity coefficient values for mono-, di- and trivalent cations indicate excellent selectivity for Cr³⁺ ions over a large number of other cations. Anions such as Cl^- and SO₄ ^2- do not interfere and the electrode also works satisfactorily in a mixed organic-water solution. The sensor has been used as an indicator electrode for the potentiometric titration of Cr³⁺ with EDTA. The practical utility of the membrane sensor has also been demonstrated in solutions contaminated with detergents (CTAB and SDS). Above all, the membrane sensor has been very successfully used to determine Cr³⁺ in some foods.