The influence of electrode polarisation on dielectric spectra, with special reference to capacitive biomass measurements. II: Reduction in the contribution of electrode polarisation to dielectric spectra using a two-frequency method

Electrode polarisation can interfere significantly with the measurement of the dielectric properties of biological systems, and in particular with the dielectric estimation of microbial biomass. We showed in the previous paper of this pair [C.L. Davey, D.B. Kell, The influence of electrode polarisation on dielectric spectra, with special reference to capacitive biomass measurements: I. Quantifying the effects on electrode polarisation of factors likely to occur during fermentations, Bioelectrochem. Bioenerg., 1998] that electrode polarisation can be modelled by a power law and that the parameters of this model can be simply modified to give reliable and intuitive measures of the magnitude (LCp)(LCp) and rate of fall of polarisation with increasing frequency (hf)(hf). Importantly and surprisingly, although the magnitude of electrode polarisation can change it was found that the hfhf value remained constant. A highly useful consequence of this constancy of hfhf for a given instrument is that one can exploit it directly to eliminate electrode polarisation from biological capacitance (or permittivity) spectra using the simple two-frequency method developed in this paper.