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Variants of Field-Flow Fractionation

To pursue fast separation we can maximize Nit, which we obtain directly from Eq. 9.19. However we follow here an alternate optimization scheme that is more like that generally applied to chromatography (Section 14.5). Following this approach, we examine the time LIT needed to bring the last component through the channel. If the separation requires N plates, then the channel length must be L = NH, in which case separation time is [Pg.211]

Thus separation time is reduced by minimizing and increasing D. It is also reduced by working with the least possible number N of plates. We minimize N by choosing the most selective FFF system this often proves to be sedimentation FFF. [Pg.211]

We see that all optimization goals depend strongly on reducing . Experimentally, values down to 1 fitn and less have been realized. Such thin solute layers yield high-speed separations, often requiring only a few minutes for completion. However with small l, particle-wall interactions increase and in some cases lead to departures from theory [25]. [Pg.211]

Normal (Nl) SdFFF E1FFF ThFFF F1FFF MgFFF DIFFF [Pg.212]

Steric (St) Sd/StFFF El/StFFF Th/StFFF Fl/StFFF Mg/StFFF DI/StFFF [Pg.212]


Figure 2 gives some characteristics of the size separation techniques that can be used to study the distribution of trace elements associated with various constituents of natural waters. It is obvious that the dimensions given in the figure are tentative as various factors influence the association/dissociation and aggregation/dispersion processes. However, preservation of real equilibria and labile species of elements, especially at concentrations of less than 10 g 1 prior to analysis is a much more serious problem encountered with methods that are not based on a direct physical separation. From this point of view, membrane filtration as well as some variants of field-flow fractionation (FFF) have advantages, although some uncertainties connected with equilibria shifts always exist. [Pg.2982]


See other pages where Variants of Field-Flow Fractionation is mentioned: [Pg.211]    [Pg.211]    [Pg.213]   


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