A polystyrene based membrane electrode for cadmium(II) ions

A polystyrene based membrane of 3,4: 12,13-dibenzo-2,5,11,14-tetraoxo-1,6,1 0,15-tetraazacyclooctadecane shows a Nemstian response to Cd(II) ions over a wide concentration range (3.16 x 10(6)-1.00 x 10(-1) mol L-1) with a Nems tian slope of 29.8 mV/decade of concentration, between pH 2.0 and 6.0. This electrode has been found to be chemically inert and of adequate stability with a response time of 20s. The electrode gives reproducible results with a lifetime of 130 days. The membrane works satisfactorily in a partially no n-aqueous medium up to a maximum 35% (v/v) content of methanol and ethanol. The practical utility of the proposed chemical sensor has been observed by using it as end-point indicator in the titration of Cd(II) ions with EDTA. The potentiometric selectivity coefficient values indicate that the membra ne sensor is highly selective for Cd(II) ions over a number of cations. Sma ll amounts of surfactants do not disturb the functioning of the sensor. Thi s electrode has also been used to estimate cadmium ions in real samples.