Electrochemical detector based on a reticulated vitreous carbon working electrode for liquid chromatography and flow injection analysis

Abstract

A new cell design for detectlon in flowing streams incorporating a reticulated vitreous carbon (RVC) worklng electrode has been Investigated. The prlnclpal feature Is geometrlcal symmetry in the radlai direction between the working eiectrode and counterelectrode. This arrangement produced weildeflned hydrodynamlc voltammograms. The reticulated structure of the worklng electrode provides a large surfacearea-to-volume ratlo whlch allows rapld coulometric conversion without slgnlflcant band broadening when the detector is used for flow injection analysis (FIA) or hlgh-performance iiquld chromatography (HPLC). The sensltivity and detection ilmlts of several test compounds were lnvestlgated In thls cell.The sensltlvlty was found to approach the theoretlcal value of 96485 CIequlv at flow rates less than 1.0 mLImln. Detection limits were close to a picoequivalent ( S I N = 2) for the compounds studied by FIA. The residual current decays In less than 30 min to a steady-state value of approximately 1 PA. Detection at the plcoequlvalent level Is possible after thls equlilbration period. Both catecholamines and amoxlcliiln were used to characterlze thls detector for use with HPLC systems.At the present time, the most widely used controlled-potential electrolysis cells for flow streams are operated amperometrically, where the fraction of electroactive species electrolyzed is typically less than 0.1. In the case of coulometric operation, the fraction is one. The methodology of applying the perturbation signal and measuring the current response is identical for coulometric and amperometric detectors. In principle, the same cell could be operated in either mode depending on the flow rate. However, in practice, the design of coulometric cells presents some special problems, and they have not achieved the same degree of popularity as the amperometric detectors. It is generally recognized that large surface area electrodes with relatively large cell volumes are required for coulometric conversion and it is generally perceived that they are not especially well-suited for applications in areas such as liquid chromatography and flow injection analysis (FIA). Two factors, perhaps, have contributed to this secondary position for coulometric detectors. The first is the lack of widespread understanding of the nature of porous electrodes and the second is a failure to recognize that the coylometric detector is a mass flow rate sensitive device. Nevertheless, porous electrodes have been examined in excellent reviews by Newman and Tiedemann (1) and by Sioda and Keating (2). Early work on coulometric detectors was reviewed by Johnson and Larochelle (3) and some recent developments regarding both amperometric and coulametric detectors have been described by Stulik and Pacakova (4). Brunt (5) and Rucki (6) have presented general reviews of Present address: . electrochemical detectors. Weber and Purdy (7) have discussed detector design and mass transfer coefficients.The objectives of this study were to design and characterize a coulometric dete...

The continued development of reticulated vitreous carbon as a versatile electrode material: Structure, properties and applications

“…Early devices were simple amperometric flow detectors [16], followed by spectroelectrochemical detectors [124]. Electrode kinetics for electroanalysis have been considered in a book edited by Compton et al [125].…”

Microporous Gold Electrodes as Combined Biosensor/Electrochemical Detectors in Flowing Streams

“…By fitting the data to the general voltammetric current-potential equation for a reversible wave [23] a half-wave potential of þ 750 mV (vs. Ag/AgCl) and an n value of 2.07 (reasonably close to the theoretical value of 2.0 expected for hydroquinone) is obtained. Measuring a value for n very close to the theoretical value suggests that the uncompensated resistance in the flow cell is very small [15].…”

“…Early porous carbon electrodes were susceptible to iR drop across the length of the electrode as well as possessing large internal volumes (up to 7.8 mL [12]). These problems were overcome by reducing the overall length of the electrode yielding porous electrodes with no significant iR drop and volumes as small as 150 mL [15]. The utility of RVC electrodes as flow through enzyme electrodes has been demonstrated for ethanol [9], and recently for catechol [10], and lactate [11].…”

Flow-Through Chronopotentiometry in Waste Water Analysis

“…Stripping analysis with matrix exchange can easily be performed by making use of a flowthrough electrochemical cell (Bard & Faulkner, 2001;Stulik & Pacakova, 1987). Moreover, porous flow-through working electrodes may open the way to achieve complete electrochemical conversions both during the deposition and the stripping steps and hence to provide calibrationless analysis just by making use of the combined Faraday's laws for signal evaluation (Blaedel & Wang, 1979;Curran & Tougas, 1984). An alternative way to provide calibrationeless determination in stripping analysis is to deposit completely the analyte from a small sample volume to a vibrating working electrode (Jagner & Wang, 1995;Jagner et al, 1996).…”