Highly thiocyanate-selective membrane electrodes based on the N,N′-bis-(benzaldehyde)-glycine copper(II) complex as a neutral carrier

Some novel PVC membrane electrodes based on N,N'-bis-(benzaldehyde)-glycine metallic complexes of Cu(II), Ni(II), Zn(II) and Co(II) as neutral carriers are described. The results showed that the electrode based on the N,N'-bis(benzaldehyde)-glycine copper(II) complex [Cu(II)-BBAG] had a near-Nernstian response to the thiocyanate ion ranging from 1.0x10(-1) to 9.0x10(-7) M in a phosphate buffer solution of pH 4.0 with a detection limit of 7.0x10(-7) M and a slope of -57.6 mV/decade at 25 degrees C. The electrode displays an anti-Hofmeister selectivity sequence in the following order: SCN-> ClO4-> Sal(-)> I-> Br-> NO-> NO2-> SO3-> SO32-> Cl-> H2PO4-. The response mechanism is discussed in view of both AC impedance and UV spectroscopy techniques. The [Cu(II)-BBAG]-based electrode was successfully applied to the determination of the thiocyanate ion in wastewater and human saliva.