Issues in Biometrics: Offset Potentials and the Electrical Stability of Ag/AgCl Electrodes

Authors


  • This research was supported by National Science Foundation Grant Nos BNS-8414853 and BNS-8517658 to ITC.

  • The authors wish to thank M. M. Ihrig for insightful and helpful comments on a previous version of this manuscript and R. Miller and L. Frei for construction of the carbon rod storage container. Portions ofthis research were presented at the 28th annual meeting of the Society for Psychophysiological Research, San Francisco, CA, October 1988.

Address requests for reprints and correspondence to: Louis G. Tassinary, Department of Psychology, University of Iowa, Iowa City, IA 52242.

ABSTRACT

There has been a continuing interest in many areas of psychophysiological research in the quantification of slow wave bioelectric potentials recorded from the surface of the skin. However, surprisingly little research has focused specifically on methods for stabilizing and minimizing the offset potentials of the sintermetallic Ag/AgCl surface electrodes commonly used in such noninvasive bioelectric measurement. To provide empirically based recommendations in this regard, we contrasted the effects of three common storage methods (air dry vs. saline vs. carbon rod) on the two distinct types of Ag/AgCl surface electrodes (sintermetallic vs. electrolytic) under simulated experimental conditions. The obtained results confirm that minimum offset potentials and maximum stability for electrolytic Ag/AgCl electrodes are obtained when they are stored in a 0.9% NaCl solution with their leads shorted together and connected in parallel to a carbon rod partially immersed in the solution (cf. Cooper, 1956). In addition, the pattern of results suggested that the inter-session unshorted storage of sintermetallic electrodes in a mild saline solution is to be recommended over either shorted saline storage in parallel with a carbon rod or unshorted dry storage.

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