Effect of Ionic and Nonionic Carriers in Electrical Field-Flow Fractionation

Abstract

A major limitation of electrical field-flow fractionation (ElFFF) is the polarization of the electrodes that occurs when using an ionic carrier liquid. As there is great interest in using ElFFF with biological materials and biological materials typically have high ionic strengths and high osmotic concentrations, we explore the effect of concentration for phosphate buffered saline (PBS), a typical ionic medium for biological samples, and for two nonionic materials common in bioparticle analysis: isopropanol (IPA) and sucrose. Their effect on retention and separations in ElFFF for increasing concentrations was observed. The results suggest that modifying the carrier solution with PBS, sucrose, and/or IPA would enable characterization and separation of biological samples in ElFFF. Specifically, changes of elution time and electrical parameters such as current, conductivity, and bulk channel resistance were observed as functions of carrier ionic and osmotic strength for the different carrier additives. PBS can be used in the micromolar range, equivalent to about 0.1% 1× PBS (150 μM). These concentrations are far from the isotonic condition of PBS (∼ 150 mM) that is normally used with biological samples. However, the nonionic additive carriers IPA and sucrose show quality retention even when added in high concentrations. The results show that IPA could be used in ratios up to 60% and that sucrose can be used in concentrations up to 0.3 M. Concentrations of 2% IPA (0.26 M) and 0.30 M sucrose are biologically isotonic conditions (275-299 mOsm/kg), and retention was readily obtained in these conditions using both DC ElFFF and cyclical ElFFF (CyE1FFF). Carriers of this type may make it possible to use ElFFF with biological samples.

Exosome Isolation: Cyclical Electrical Field Flow Fractionation in Low-Ionic-Strength Fluids

“…Aside from influencing the electrophoretic mobility of the particles, salt concentration also greatly affects the effective field. Previous work showed that even small amounts of salt in the 15–750 μM range can greatly affect separations using a DC separation voltage in El-FFF. The use of cyclical AC voltages in El-FFF may overcome some of the detrimental effects of salt, because AC voltages produce a higher effective field; therefore, this study used AC fields to perform separations.…”

“…One difficulty in using El-FFF for biological vesicle separation is that salt concentration within typical physiological vesicle buffers is high enough to reduce the strength of the effective electric field within the El-FFF channel . Salt must be removed via buffer substitution if effective vesicle separation using El-FFF is to be achieved.…”

Label-Free Isolation of Exosomes Using Microfluidic Technologies

“…263 Although the FFF technology presents a highly promising, label-free approach to separate EVs based on their physical properties, extensive optimization is required to perform an efficient separation. 256,263,246 Pinched Flow Fractionation. Pinched flow fractionation (PFF) is another flow-driven separation technique originally proposed by Yamada et al, 264 implemented for particle separation in microfluidic devices.…”

Field‐flow fractionation for nanoparticle characterization

“…CyElFFF was used to determine the electrophoretic mobility of carbon-based NPs [18,28,29]. Significantly different electrophoretic mobility distributions were obtained for single-walled carbon nanotubes with similar size distributions; this was attributed to their different graphene sheet winding structures, that is, their different chirality [19].…”