Effect of Carrier Fluid Viscosity on Retention Time and Resolution in Gravitational Field-Flow Fractionation

Abstract

Gravitational field-flow fractionation (GrFFF) is a useful technique for fast separation of micrometer-sized particles. Different sized particles are carried at different velocities by a flow of fluid along an unobstructed thin channel, resulting in a size-based separation. They are confined to thin focused layers in the channel thickness where force due to gravity is exactly opposed by hydrodynamic lift forces (HLF). It has been reported that the HLF are a function of various parameters including the flow rate (or shear rate), the size of the particles, and the density and viscosity of the liquid. The dependence of HLF on these parameters offers a means of altering the equilibrium transverse positions of the particles in GrFFF, and hence their elution times. In this study, the effect of the viscosity of the carrier fluid on the elution behavior (retention, zone broadening, and resolution) of micrometer-sized particles in GrFFF was investigated using polystyrene (PS) latex beads as model particles. In order to change the carrier liquid viscosity without affecting its density, various amounts of (hydroxypropyl) methyl cellulose (HPMC) were added to the aqueous carrier liquid. It was found that particles migrate at faster rates as the carrier viscosity is increased, which confirms the dependence of HLF on viscosity. At the same time, particle size selectivity decreased but peak shape and symmetry for the more strongly retained particles improved. As a result, separation was improved in terms of both the separation time and resolution with increase of carrier viscosity. A theoretical model for plate height in GrFFF is also presented, and its predictions are compared to experimentally measured values.

Size Selectivity in Field-Flow Fractionation: Lift Mode of Retention with Near-Wall Lift Force

“…It has been recently observed that the size selectivity in SdFFF increases with increasing carrier viscosity. 47 This is expected because, according to eq 24, an increase in viscosity leads to an increase in φ eq , hence, as seen in Figure 3a, to an increase in S d , whatever the particle size.…”

“…Experimental S d values reported in the literature vs reference number: (a) SdFFF data; ,,− (b) FlFFF data. ,− …”

“…The dependence of band broadening on operating parameters may lead to a shift of the values of the optimal conditions. This dependence has been recently investigated for lift mode operation in gravitational FFF …”

“…This dependence has been recently investigated for lift mode operation in gravitational FFF. 47 Effect of Channel Thickness on Size Selectivity. Decreasing the FFF channel thickness is often advocated as an approach for improving separation performances.…”

Adverse-Mode FFF: Multi-Force Ideal Retention Theory

“…The flexibility of FFF results from the large number of potential transverse external fields that can be used. Gravitational [23,24], centrifugal sedimentation [25,26], electrical [27,28], magnetic [29,30], dielectrophoretic [31,32], acoustic [33,34], photophoretic [35,36], cross-flow (both symmetrical [37,38] and asymmetrical [39,40]) and thermal [41,42] fields have all been utilized by FFF. Cross-flows (both symmetrical and asymmetrical), sedimentation and thermal gradients are the most commonly-employed fields.…”