Electrode polarization impedance in saline

The series capacitances of some other metal/electrolyte interfaces are given by Geddes (1972). They are always lower than the AgCl or platinum black electrodes in 0.9% NaCl. For. stainless steel, it was given as 40 pF/cm at 20 Hz ( = 500 pS/cm ). 

Tlie series resistance in these models may be regarded as an access resistance to the electrode interface, dependent on electrolyte conductivity and geometry, but not linked to the polarization processes. As such it belongs to the chapter on contact media, and should be subtracted from measured electrode impedance when analyzing polarization immittance. 

Difference between Electrolyte and Tissue as Contact Media 

A contact eleclroljrte is a homogeneous material. The current distribution may be uniform with the metal closing the cross-sectional area of a measuring cell tube. Otherwise, it will 

A polarization ratio can he defined as the ratio of polarization impedance to the bulk resistance of the electrolyte. Mirtaheri et al. (2005) measured the ratio as a function of frequency (10 —10 Hz) and NaCl concentration (2.4—77.0 mmol/L) and found that the polarization ratio diminished as a function of concentration regardless of electrode material. Medical stainless steel ratio was concentration independent hut had high electrode polarization impedance values compared with the other metals studied. Aluminum showed small ratio changes at low concentrations. However, the changes were more pronounced at higher concentrations. Gold, platinum, and silver showed a moderate concentration dependency at low concentrations. 

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