Carlos F. P. MIRANDA1, Luís M. N. B. F. SANTOS1
1CIQUP, Institute of Molecular Sciences (IMS), Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, Porto, Portugal
Electrical conductivity measurements at a fixed frequency are intrinsically affected by polarization effects. Although high frequencies dimmish the impact of the polarization effect, it raises other problems associated with parasitic effects. Therefore, measuring impedance across a wide range of frequencies is the state-of-the-art procedure [1].
This work presents the development of a new system for the high precision measurement of electrical conductivity of ionic fluids. The measuring system is based on a Precision LCR meter (20 Hz - 500 kHz) from Keysight (model E4980AL). The measuring cell is composed by an adapted Metrohm electrical conductivity cell (model MTO-6.0908.110), a small sample glass vessel (8 mL) and a customized holder which was specially designed to insure the vacuum, gas-tight and chemical inertia of the sample container. The system is equipped with vacuum / N2 (g) lines which allows the degassing and atmospheric isolation of the sample. The temperature control is ensured by a customized air bath thermal chamber based on Peltier heat and cooling. A dedicated software application was developed for data acquisition and analysis as well as to configurate the setup for the measurements.
The results are evaluated in terms of resistance, reactance, impedance, and phase angle as functions of frequency. The correction for the polarization effect is performed using several extrapolation procedures. The extrapolation is carried by selecting the appropriate frequency range which corresponds to a region of resistance-frequency linearity.
The cell constant was experimentally determined by measuring standard aqueous 0.1 and 0.01 molal KCl solutions at different temperatures. The effects of the electrical potential level, N2(g) flow and cell immersion depth on the temperature and signal stability were evaluated for KCl solutions and ionic liquids. The accuracy of the apparatus was evaluated by measuring a series of reference ILs.
Acknowledgements
This work was supported by the Fundacão para a Ciência e Tecnologia (FCT) through the FCT/MCTES (PIDDAC) to CIQUP, Faculty of Science, University of Porto (Project UIDB/00081/2020),
IMS-Institute of Molecular Sciences (LA/P/0056/2020). Carlos F. P. Miranda is grateful to FCT for his research grant (Reference: 2020.05717.BD).
References
[1] X. Paredes, C. S. G. P. Queirós, F. J. V. Santos, A. F. Santos, M. S. C. S. Santos, M. J. V. Lourenço and C. A. N. d. Castro, J. Phys. Chem. Ref. Data, 49 (2020) 043101.
[2] K. W. Pratt, W. F. Koch, Y. C. Wu and P. A. Berezansky, Pure Appl. Chem. 73 (2001) 1783-1793.