Enhancing resolution of free‐flow zone electrophoresis via a simple sheath‐flow sample injection

Abstract

In this work, a simple and novel sheath-flow sample injection method (SFSIM) is introduced to reduce the band broadening of free-flow zone electrophoresis separation in newly developed self-balance free-flow electrophoresis instrument. A needle injector was placed in the center of the separation inlet, into which the BGE and sample solution were pumped simultaneously. BGE formed sheath flow outside the sample stream, resulting in less band broadening related to hydrodynamics and electrodynamics. Hemoglobin and C-phycocyanin were successfully separated by the proposed method in contrast to the poor separation of free-flow electrophoresis with the traditional injection method without sheath flow. About 3.75 times resolution enhancement could be achieved by sheath-flow sample injection method.

Investigating peak dispersion in free‐flow counterflow gradient focusing

“…This is especially true for larger sample injection widths, as they will require longer focusing times that may not be feasible for a given chamber length. On another note, it would also be helpful to consider situations where the sample injection is focused in the height direction [40], as this could limit peak tailing at large $${G_x}$$ values. Interestingly, the mixing parameter $$d$$ can provide a useful reference for the level of focusing that is required in the height direction to mitigate the peak tail.…”

A microchip device to enhance free flow electrophoresis using controllable pinched sample injections

“…Recently, several strategies were presented to reduce the hydrodynamic broadening from analyte deflection and parabolic pressure driven flow profile nature [26,27]. Spatially controlled injection turned out to be a theoretically effective strategy for resolution enhancement in both macro-and micro-scale free flow electrophoresis [27,28]. However, diffusion broadening of analyte at the exit of the separation chamber can destroy the spatially controlled injection, especially at low flow rate conditions.…”

A review of the zone broadening contributions in free‐flow electrophoresis

“…For example, although the contributions to the stream variance (𝜎 2 ) from the injection and lateral diffusion processes are well established, there are no reports detailing how this quantity can be expected to evolve with the separation length prior to attaining the TA dispersion limit. Such an analysis is especially relevant to assays that rely on spatially confined stream injections and short separation times [48,49]. Additionally, the influence of the stream size and location at the channel entrance on this evolution process and zone symmetry is lacking in the literature.…”

“…Thus, this limit is realized for $$L\gg 0.25\ \mathrm{cm}$$ when$$\ {\bar{U}}_{p}=\ 1\ \mathrm{cm}/\mathrm{s}$$, $$d\ =\ 10\ \mu \mathrm{m}$$ and $$D\ ={10}^{-6}\ \mathrm{c}{\mathrm{m}}^{2}/\mathrm{s}$$ which is often satisfied for miniaturized FFE systems. In a couple of recent reports, however, researchers have proposed a novel injection strategy in which the sample stream was introduced only over a fraction of the channel depth to minimize the hydrodynamic dispersion of the analyte zones [48, 49]. This strategy allows the advection of the analyte stream through a region of the PDF field where the variations in the streamline velocity are relatively small.…”