Correcting the polarization effect in very low frequency dielectric spectroscopy

Polarization impedance appears at the interface between electrodes and ionic solutions and is a major source of errors in dielectric spectroscopy measurements. This work presents a simple, robust and automated methodology for measuring and analysing the polarization impedance of non-dispersive electrolytes, with a focus on the very low frequency domain from 1 Hz and up. The accuracy of the method is demonstrated by comparing the corrected dielectric permittivity and conductivity of various electrolytes either with their nominal values or with measurements taken with other high precision measuring devices. The dependence of the polarization impedance on several parameters, such as ionic concentration, applied voltage and separation distance between the electrodes, is also presented. For colloidal suspensions, it is argued that a modified protocol of the substitution method is needed due to several shortcomings occurring only in the very low frequency domain. Such a protocol is presented and tested on suspensions of live E. coli cells. As opposed to most of the existing methodologies for polarization removal, the proposed protocol makes no assumptions on the behaviour of the polarization impedance. This could potentially lead to the quantitative resolution of the α-dispersion of live cells in suspension. (Some figures in this article are in colour only in the electronic version)