Traceability of electrolytic conductivity measurements to the International System of Units in the sub mS m−1 region and review of models of electrolytic conductivity cells

The present paper focuses on the currently available reliability of the results of electrolytic conductivity measurements in the low conductivity range, emphasizing its weaknesses with respect to SI traceability. Electrochemical and physical effects at the electrode–solution interface influencing the measured impedance spectra are outlined, giving an overview of models that can be employed to investigate the frequency response of electrolytic conductivity cells to an applied AC voltage. Particular attention is devoted to the determination of the bulk resistance of the solution, which is necessary to derive the electrolytic conductivity of aqueous solutions traceable to the SI in the sub mS m−1 range.