Mercury(II)-selective membrane electrode using tetrathia-diazacyclotetradeca-2,9-diene as neutral carrier

Polystyrene-based membrane of 2,3,4,9,10,11-dipyridine-3,10-diaza-1,5,8,12-tetrathiacyclotetradeca-2,9-diene with sodium tetraphenyl borate (STB) and dibutyl phthalate (DBP) as anion excluder and plasticizing agent was prepared and investigated as Hg(II)-selective electrode. The best performance was observed with the membrane having the ligand–polystyrene–DBP–STB composition 1:4:1:1 with a Nernstian slope of 30.0 mV per decade of concentration between pH 2.5 and 5.0. This electrode has been found to be chemically inert and of adequate stability with a response time of 18 s and was used over a period of 120 days with good reproducibility (S=0.3 mV). The membrane works satisfactorily in a partially non-aqueous medium up to a maximum 30% (v/v) content of methanol and ethanol. The practical utility of the proposed chemical sensor has been observed by using it as an end-point indicator in the titration of Hg(II) ions with EDTA. The potentiometric selectivity coefficient values indicate that the membrane sensor is highly selective for Hg(II) ions over a number of monovalent, divalent and trivalent cations.