Novel plastic chromium (III)-ion selective electrodes based on different ionophoric species and plasticizing solvent mediators

Different ionophoric species, viz.: 18-crown-6 (18C6), dibenzo-18-crown-6 (DB18C6) and calix[6]arene (CAX), as electroactive materials, with 2-nitrophenyloctylether (2-NPOE), bis(ethylhexyl)sebacate (DOS), dioctyl phthalate (DOP), and didecyl phthalate (DDP) as plasticizing solvent mediators were used to construct Cr3+ selective electrodes in a PVC matrix in the ratio (w/w) PVC: ionophore: plasticizer (60:2:120). Seven electrodes out of the fabricated 12 electrodes, gave best results in terms of working concentration range (1.0 x 10(-5) - 1.0 x 10(-1) M) with a close to Nernstian slope of 18.5 and a Nernstian slope of 20.0 mV/decade of activity. The usable pH range of the sensors is 4.0 - 7.0. The detection limit of the selected electrodes is <= 1.0 x 10(-7) M. The response time of the sensors is 8 - 35 s, depending on the concentration of Cr3+ used. The selectivity coefficient values indicate that the electrodes are highly selective for Cr3+ over a number of other cations except Pb2+ and Na+ (for some electrodes). The electrodes have successfully been used to determine Cr3+ in certified and real alloys and in effluents of electroplating shops with a precision as relative standard deviation (RSD) < 3%, for each of the proposed Cr3+-ion selective electrodes. The results obtained by the proposed ISEs are in good agreement with the results obtained by direct flame AAS method.