Graphene layer modified glassy carbon electrode for the determination of norepinephrine and theophylline in pharmaceutical formulations

In this paper, electrochemical determination of norepinephrine (NE) and theophylline (TP) was demonstrated using an electrochemically reduced graphene oxide (ERGO) modified glassy carbon electrode (GCE). The ERGO was fabricated on a GCE by self-assembling graphene oxide (GO) on 1,6-hexadiamine (HDA) which was preassembled on the GCE, followed by the electrochemical reduction of GO. SEM imaging shows a flake-like structure for the GO modified substrate, whereas an aggregated structure was observed for the ERGO modified substrate. Then, the ERGO modified GCE was used for the determination of NE and TP. It was found that the ERGO modified electrode not only enhanced the oxidation currents of NE and TP, but also prevented a surface fouling effect caused by their oxidation products. In contrast, the oxidation currents of both NE and TP were low at bare and GO modified GCEs and very importantly, their oxidation signals were not stable due to the surface fouling effect. The ERGO modified GCE separated the oxidation signals of NE and TP in a mixture and was hence used for their simultaneous determination. Selective determination of NE in the presence of a higher concentration of TP was also achieved at an ERGO modified GCE. Using amperometry, a detection of 40 nM NE and 50 nM TP was obtained. The current responses of NE and TP were increased linearly while increasing their concentrations from 4 x 10(-8) to 1 x 10(-4) M and 5 x 10(-8) to 4 x 10(-5) M and the detection limits were found to be 8.4 x 10(-10) M and 2.9 x 10(-9) M (S/N = 3), respectively. The practical application of the present modified electrode was demonstrated by measuring the amounts of NE and TP in injections and tablets.