Fabrication and characterization of copper ring-disk microelectrodes for capillary electrophoresis

Tungsten ring-disk microelectrodes were constructed by two Chemical Vapor Deposition with Resistive Heating techniques: atmospheric and low pressure. This method allows for the deposition of a wide variety of conductors or insulating materials directly onto a resistively heated substrate, creating concentric thin-films with excellent adhesion to the substrate surface. Alternating layers of silica and tungsten were deposited onto a 25 pm diameter tungsten wire (which served as the disk portion of the electrode) for an overall diameter of approximately 60 mum. Films were characterized by energy dispersive spectroscopy and X-ray powder diffraction. Tungsten microelectrodes were then embedded in pulled glass pipettes and characterized by voltammetry, microscopy, and scanning electron microscopy.;Several electrochemical techniques were utilized to chemically modify the tungsten surface with copper. Constant Overpotential (CO) and Pulsed Overpotential (PO) waveforms were applied at the tungsten surfaces to etch and subsequently fill the remaining microcavity with copper. The resulting copper microelectrodes were then electrochemically tested for their potential use as amperometric detectors for carbohydrates and similar biological molecules.;Dual electrochemical detection with capillary electrophoresis has shown great versatility for the analysis of complex mixtures. Two or more working electrodes provide added selectivity and a new host of detection schemes that enable peak purity determination for comigrating species and elimination of interferences previously unattainable with single electrode detection. Good linearity between carbohydrate concentration and current response in flow injection studies demonstrate the copper ringdisk microelectrode as a dual amperometric detector for capillary electrophoretic separations.