Hydrodynamic relaxation and sample concentration in field-flow fractionation using permeable wall elements.
Hydrodynamic relaxation and sample concentration in field-flow fractionation using permeable wall elements.
复制标题
使用渗透壁元件进行场流分馏中的流体动力学松弛和样品浓度。
DOI：
10.1021/ac00220a010
复制
发表时间：
1990
影响因子：
7.4
通讯作者：
Giddings,JC
中科院分区：
文献类型：
--
作者：
Giddings,JC
The advantages of hydrodynamic relaxation in field-flow fractionation, in which an injected sample Is driven rapidly toward its equilibrium distribution by flow, are described relative to conventional field-driven relaxation. A new concept for achieving hydrodynamic relaxation, based on the use of permeable wall elements (or frit elements) embedded in the channel walls, Is introduced. Here an auxiliary substream of carrier fluid, permeating uniformly Into the FFF channel near the inlet, drives the sample, entrained in its own substream, close to its equilibrium configuration. Such frit elements can also be used to enrich the sample at the outlet. Equations are derived and plots are provided for the position of the splitting plane dividing the two substreams; this position defines the strength of the hydrodynamic relaxation. Variations in shear through these frit-modified end regions are also formulated and plotted. The effects of frit elements on band broadening are discussed. It Is concluded that permeable wall elements in many configurations may be broadly applicable to FFF and related methods for improved sample in-troduction, increased separation speed, reduced risk of sam-ple adhesion to the wall, Improved flow stability, and sample enrichment.In virtually any kind of field-flow fractionation (FFF) process, a relaxation step must be carried out in the FFF channel prior to the beginning of effective separation (1-3). In the relaxation process, sample material that is distributed widely over the streamlines entering the channel is forced into narrow cross-sectional distributions from whichseparation is possible. Normally, a sample is driven close to one wall (the accumulation wall) of the channel during relaxation by the same external field or gradient that is used to implement FFF separation. In most cases the axial flow is halted, as relaxation takes place in order to control band distortion and broadening. This so-called stopflow procedure sometimes leads toflow instabilities accompanied by baseline shifts and provides a window of vulnerability in which sample particles are most susceptible to adhesion to the channel wall. It also increases run time. Consequently, means have been pursuedrecently for introducing samples into FFF channels without stop flow operation (4, 5).
