Fast Cyclic Voltammetry

Many electrochemists are interested in the application of fast cyclic voltammetry (FCV), where the scan rate is very high (>100 V/s). In a typical experiment, a triangular wave is imposed on a working electrode (WE) and the current response is recorded as a function of the WE potential, as measured versus a reference electrode. An analysis of the current vs potential (i-E) wave provides both thermodynamic and kinetic information about the electrode reaction.[1]

FCV is most applicable to microelectrodes, where the diameter (d) determines the optimal scan rates in terms of the signal-to-noise (S/N) ratio. Although both the faradaic current (I_f) and capacitive current (I_c) decrease as d (and area) decrease, the ratio of I_c/I_f is a function of d and the scan rate, as seen in Table 1.

Table 1.
Optimal scan rates for electrodes of different sizes (1 mM solution)

NOTE: The lower limit criterion is that the spherical diffusion current is less than 5% of the linear diffusion current (values shown for D=10^-5 10^-6 cm²/s. The upper limit criterion is based on an iR loss of 10/100 mV (assuming R=1,000). The ratio of capacitive to faradaic current is also given for the faster scan rate. At the fastest scan rates it is advisable to use higher concentrations, about 0.01 M.

Reprinted by permission of John Wiley & Sons, Inc. See reference 1.

The 66-CS1200 and the 66-EI400 are potentiostats with FSV capabilities. Microelectrodes are easily implemented and are relatively inexpensive.[2] Cypress has available 10 µm diameter glassy carbon, Pt and Au microelectrodes.

The most commonly used scan rate with microelectrodes centers around 300 V/s. The combination of FCV and microelectrodes can be employed to do in vivo studies at subsecond time resolution [3] or to detect neurotransmitters, e.g., dopamine (DA) or 5-hydroxytryptamine (5-HT) in vivo.[4] For in vivo analysis, carbon fiber microelectrodes are more commonly used than other electrode materials because of their compatibility with biological tissues.[5] Moreover, Nafion-coating of the carbon fibers has minimized interference from ascorbate and uric acid allowing improved specificity for DA. Futher details and applications of FCV with microelectrodes are described in reviews by Stamford [6] and Kawagoe, et. al.[7]

References

• Gosser, D. K. Jr, Cyclic Voltammetry: Simulation and Analysis of Reaction Mechanisms, VCH (1993).
• Pons, S. and M. Fleischmann, "The Behavior of Microelectrodes," Anal. Chem., 59, 1391A-1399A (1987).
• Wiedemann, D.J., K.T. Kawagoe, R.T. Kennedy, E.L. Ciolkowski, and R.M. Wightman, "Strategies for Low Detection Limit Measurements with Cyclic Voltammetry," Anal. Chem., 63, 2965-2970 (1991).
• Jackson, B.P., S.M. Dietz, and R.M. Wightman, "Fast-Scan Cyclic Voltammetry of 5-Hydroxytryptamine," Anal. Chem., 67,1115-1120 (1995).
• Wightman, R.M., L.J. May, and A.C. Michael, "Detection of Dopamine Dynamics in the Brain," Anal. Chem., 60, 769A-779A (1988).
• Stamford, J.A.,"In Vivo Voltammetry," Methods in Neurosciences, Vol. 4, pp 127-142, Academic Press (1991).
• Kawagoe, K.T., J.B. Zimmerman, and R.M. Wightman, "Principles of Voltammetry and Microelectrode Surface States," J. Neuroscience Methods, 48, 225-240 (1993).
  

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