Electrochemical modification of benzo-15-crown-5 ether on a glassy carbon electrode for alkali metal cation recognition

Benzo-15-crown-5 (B15C5) was covalently immobilized on a glassy carbon (GC) electrode and its complexation ability with alkali metal cations was studied. A mixture of 4′-aminobenzo-15-crown-5 and NaNO2 was prepared to generate diazotized B15C5, and a GC electrode was immersed in the mixture. By potential cycling between 0.0 and −0.8 V, the diazotized B15C5 was reduced electrochemically and reacted with the carbon atoms at the electrode surface to form the B15C5 layer on the GC electrode. Cyclic voltammetry and scanning tunneling microscopy were used to characterize the B15C5 layer. The surface amount of B15C5 groups increased by repeating the potential cycles, and reached a saturated value within 20 cycles. STM observation reveals that a monolayer or sub-monolayer of B15C5 was formed. The adsorption behavior of alkali metal cations to the B15C5 layer on GC electrode was examined by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The order of adsorption constants was K+ > Na+ > Rb+ > Li+ > Cs+, indicating cooperative association between K+ and B15C5 groups at the modified electrode surface.