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

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 show 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 (LCpLCp) and rate of fall of polarisation with increasing frequency (hfhf). Importantly and surprisingly, although the magnitude of electrode polarisation depends strongly on the conductance of the medium and the material of the electrodes, above a certain value of medium conductance (of some 3–7 mS, conductivity=3.7–8.7 mS cm−1), the value of hfhf is a constant and independent of the conductance of the medium. It is also independent of the electrode metal in the probes, which probe was used, the ionic and other components in the medium, the electrode interface current density, the cell constant, the presence of fouling materials and whether or not any electrolytic cleaning pulses had been applied. This permits one simply to correct for the electrode polarisation present in dielectric spectra and which may sometimes be seen during dielectric biomass measurements.