In tissue impedance measurements with the 4-electrode assembly, unexpected difficulties may occur because a combination of electrode impedance and stray capacitance in the array of four electrodes, can lead to serious measuring failures in the low-frequency range. An optimal solution to this problem can be obtained if the electrode impedances are frequency independent. A comparative study of the electrode impedances of Pt and PtIr electrodes and of a new electrode material (Ir-AIROF) is reported. It is shown that the impedance of Ir-AIROF electrodes is relatively low and almost frequency independent. Therefore the use of Ir-AIROF electrodes provides a solution to the problem mentioned above.
Gielen, F. L. H., & Bergveld, P. (1982). Comparison of electrode impedances of Pt, PtIr (10% Ir) and Ir-AIROF electrodes used in electrophysiological experiments. Medical & biological engineering & computing, 20(1), 77-83. https://doi.org/10.1007/BF02441854