A novel method for effective field measurements in electrical field‐flow fractionation

Abstract

The electric field that drives separation and retention in electrical field flow fractionation (ElFFF) and cyclical electrical field-flow fractionation (CyElFFF) is a complex function of many parameters such as carrier ionic strength and pH, voltage, channel dimensions, flowrate, and electrode material. Currently there is no accurate or in situ method to measure the field during system operation. This paper introduces a technique to measure the effective electric field during ElFFF and CyElFFF operation using transient electrical spikes. With this technique we can determine the relationship between changes in carrier conductivity and flowrate during a run and their combined effect on effective field and retention in ElFFF. This technique can also be used to measure the voltage drop due to double layer capacitance in CyElFFF and the variation in effective field with frequency of the applied field. The measured effective fields for the CyElFFF and DC ElFFF techniques are also tested with a high ionic-strength buffer solution as carrier. For a high ionic-strength buffer, DC ElFFF generates a near-zero effective field (0.2% in 100 s), whereas CyElFFF can sustain much higher effective fields (~8%) even at relatively high voltages. The ability to measure the effective field allows for experiments to provide better data and for tuning and optimization of the separation run.

Characterization of Polymerized Liposomes Using a Combination of dc and Cyclical Electrical Field-Flow Fractionation

“…As accuracy of both the ElFFF and CyElFFF methods depends on these field measurements, both the diameter and electrophoretic mobility measurements using these techniques would improve if a continuous field measurement technique was available. Recent work suggests that a continuous field measurement may be possible, and applying this technique to work similar to this may result in even better measurements than those shown here.…”

Label-Free Isolation of Exosomes Using Microfluidic Technologies

“…251−254 However, separation performance in constant voltage operation was limited due to the induced polarized layer on the surface of electrodes which weakened the effective electric field. 242,249,255,256 To increase the effective electric field, a pulse reversing technique was introduced as an alternative approach to discharge the polarized layer, thereby improving separation performance. 242,249,257−259 Using the pulsed voltage strategy, it is possible to optimize the retention behavior of nanoparticles via parameters such as pulse frequency, duty cycle, and waveform.…”

“…The balancing of these forces (electrical and diffusion) brings particles to a particular lamina of the parabolic flow profile, which is dependent on the particle size and electrophoretic mobility. As a result, different particles travel at different speeds in the microchannel and can be separated based on the time they leave the channel. − Electrical-FFF technology has been extensively used for separating nanoparticles over a broad size range according to their distinct electrophoretic mobility (Figure C). − However, separation performance in constant voltage operation was limited due to the induced polarized layer on the surface of electrodes which weakened the effective electric field. ,,, To increase the effective electric field, a pulse reversing technique was introduced as an alternative approach to discharge the polarized layer, thereby improving separation performance. ,,− Using the pulsed voltage strategy, it is possible to optimize the retention behavior of nanoparticles via parameters such as pulse frequency, duty cycle, and waveform. For example, Lao et al .…”

Particle Based Modeling of Electrical Field Flow Fractionation Systems

“…In most of CyElFFF studies 50% duty cycle voltage waveforms were used as the input voltages [4,8,[15][16][17][18]26,27]. Recently it has been shown that using higher duty cycle waveforms produces longer retention times [28].…”