Effect of Introducing Nonideal Capacitance in the Estimation of the Solution Resistance for Accurate Electrolytic Conductivity Measurements

[Image: see text] The standardization of secondary electrolytic conductivity cells requires the use of a certified reference material. The accepted certification method involves electrochemical impedance spectroscopy (EIS) to estimate the material’s solution resistance. This method normally assumes that the impedance’s imaginary component can be neglected; and hence, the measured impedance approximates the real impedance. Thus, a linear extrapolation of the impedance versus the period (inverse frequency) yields solution resistance. However, experimental impedance data usually do not exhibit a linear behavior over the spectra of frequency, which strongly suggest that the ideal capacitive assumption may not strictly apply. To account for the observed nonlinear behavior, we have proposed to introduce the concept of a constant phase element (CPE) to the analysis of impedance. This approach leads to the development of a relationship that improves the fitting of experimental data and improves the accuracy of the estimation, by establishing a critical frequency where extrapolation should be done. Finally, we are presenting simulated results to demonstrate how sizeable capacitive effects can influence the determination of solution resistance, and a final analysis to estimate the impact on constant cell or electrolytic conductivity values.