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Measurement of Ion-Pairing Interactions in Buffer Solutions with Microwave Microfluidics

Published

Author(s)

Charles A. Little, Angela C. Stelson, Nathan D. Orloff, Christian J. Long, James C. Booth

Abstract

Broadband microwave microfluidics is an emerging technique for quantifying the frequency dependent electrical response of fluids in the microwave regime. This technique can access important physical properties including interfacial polarization, ion mobility, and hydration. Many biologically and chemically relevant materials require buffer solution, which containing ions. Here, we show that the presence of ions in solution produces a weak ion-pairing signal. We used microfluidics integrated with coplanar waveguides, in combination with a hybrid microwave calibration protocol, to extract the broadband microwave spectra of a standard TAE-Mg2+ buffer solutions between 100 kHz – 67 GHz. To characterize the ion-pairing signal, we fit the calibrated data with two models: a conventional model without ion-pairing and with a water relaxation described by a Cole-Cole function, and our alternative model that includes ion-pairing and a single Debye-type water relaxation. We found an improved goodness of fit for the new model where ion-pairing was included. The measurement and fitting techniques are broadly applicable to all ionic solutions, and provide critical information about the behavior of solvated ions, specifically relevant for microbiological systems.
Citation
IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology

Keywords

Permittivity measurement, Microfluidics, Transmission line measurements, Coplanar waveguides

Citation

Little, C. , Stelson, A. , Orloff, N. , Long, C. and Booth, J. (2019), Measurement of Ion-Pairing Interactions in Buffer Solutions with Microwave Microfluidics, IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=926361 (Accessed April 13, 2024)
Created January 1, 2019, Updated October 3, 2019