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Issues in biometrics: offset potentials and the electrical stability of Ag/AgCl electrodes
L G Tassinary1, T R Geen, J T Cacioppo
1Department of Psychology, University of Iowa, Iowa City 52242.
Psychophysiology
|March 1, 1990
Summary
Properly storing silver/silver chloride (Ag/AgCl) electrodes is crucial for accurate psychophysiological research. Electrolytic Ag/AgCl electrodes perform best when stored in saline with shorted leads, while sintermetallic electrodes benefit from unshorted saline storage between sessions.
Area of Science:
- Psychophysiological research
- Bioelectric potential measurement
- Electrode artifact reduction
Background:
- Quantification of slow wave bioelectric potentials from skin surface is vital in psychophysiology.
- Offset potentials and stability of silver/silver chloride (Ag/AgCl) surface electrodes are critical for accurate noninvasive bioelectric measurements.
- Limited research exists on optimal storage methods for minimizing electrode offset potentials.
Purpose of the Study:
- To investigate and compare the effects of different storage methods on Ag/AgCl electrode performance.
- To provide empirically-based recommendations for stabilizing and minimizing offset potentials in Ag/AgCl electrodes.
- To contrast storage effects on sintermetallic versus electrolytic Ag/AgCl electrode types.
Main Methods:
- Simulated experimental conditions were used to test three common storage methods: air dry, saline, and carbon rod.
- Two distinct Ag/AgCl electrode types (sintermetallic and electrolytic) were evaluated.
- Offset potentials and stability were measured under each storage condition.
Main Results:
- Electrolytic Ag/AgCl electrodes exhibited minimum offset potentials and maximum stability when stored in 0.9% NaCl solution with leads shorted and connected in parallel to a carbon rod.
- Sintermetallic electrodes showed better performance with inter-session unshorted storage in a mild saline solution compared to other methods.
- Unshorted dry storage was found to be less effective for sintermetallic electrodes.
Conclusions:
- Optimal storage protocols differ between electrolytic and sintermetallic Ag/AgCl electrodes.
- For electrolytic electrodes, saline storage with shorted leads and a carbon rod is recommended.
- For sintermetallic electrodes, unshorted storage in mild saline solution between sessions is advised for improved stability and reduced offset potentials.