Selective determination of dopamine using unmodified, exfoliated graphite electrodes

Selective determination of a neurotransmitter, dopamine (DA), is achieved in the presence of ascorbic acid (AA) at neutral pH on an inert, unmodified exfoliated graphite electrode. The edge planes, exposed by roughening the surface of the electrode have been found to be very active for electrochemical sensing. A separation of 0.24 V in the oxidation potential and an increase of 100 times in the currents between DA and AA have been observed with the graphite exfoliated at 800 degreesC. The exfoliation temperature is found to play a major role in determining the activation of the surface and in turn the effective separation of the analytes. This is attributed to the trend in the O/C ratios on the graphite electrodes observed using X-ray photoelectron spectroscopy. The separation is mainly due to the repulsive interactions between the functional groups on the electrode surface and the ascorbate anion. This is confirmed by comparing the point of zero charge (pH(PZC)) of the electrode surface determined using pH titration and the pK(a) of AA. A very low detection limit of 50 nM of DA in the presence of 100 muM ascorbic acid has been observed using chronoamperometry. The exfoliated graphite is an unmodified electrode and hence just polishing the electrode could expose the active surface. The analytical utility of the exfoliated graphite electrodes for the selective determination of DA in the presence AA is presented. (C) 2003 Elsevier B.V. All rights reserved.