Flow field flow fractionation in hollow cylindrical fibers

Abstract

problems. First, certain bonded phases change in nature as well as in the amount of stationary phase; both of these effects result in irreproducible separations. Second, the degradation products from the bonded phase can contaminate a fraction isolated during a separation; such adulteration is of special consideration in preparative chromatography.We have developed two new classes of bonded phases that result in significantly increased stability of HPLC column packings during use. The first class uses bifunctional (or bidentate-type) silanes, which contain one reactive site on each of two silicon atoms of the silane. These two silicon atoms are connected by a bridging group, such as -Oor -(CH2)"-The type of bridging group can be varied, to change the spacing between the silicon atoms of the silane for the most favorable reaction with the SiOH groups on the surface of silica supports. Bonded-phase packings with methyl, vinyl, phenyl, isopropyl, and tert-butyl functional groups show similar properties-but greater stability at low pH-than their corresponding dimethylsilyl derivatives.A second class of more stable bonded-phase materials uses monofunctional silanes, which contain one or two bulky groups (e.g., isopropyl or tert-butyl) on the silicon atom of the silane. These bulky groups provide steric protection to the Si-O-Si bond on the surface of the silica supports against hydrolysis at low pH, while still providing equivalent retention and column efficiency, compared to those of conventional monofunctional silane bonded-phase packings.ACKNOWLEDGMENT Special thanks are given to R. F. Carver for performing the solid-state NMR experiments. We also thank G. R. Wooler and J. B. Marshall for their work in performing many of the syntheses and chromatographic experiments.

Practical experience with organic solvent flow field-flow fractionation

“…Figure 1 shows a scanning electron microscopy (SEM) image of an asymmetric polysulphone membrane. Lee et al [8] and later J6nsson and Carlshaf [9] showed that porous hollow fibres can be used as membranes for flow FFE In previous work in our laboratory [10,11], we Table I. For each type at least three membranes were tested.…”

Characterization of magnetic nanoparticles using programmed quadrupole magnetic field-flow fractionation

“…It was noted above that FFF optimally requires the field and/or field gradient to be uniform across the breadth of the channel, and that the channel also be of uniform thickness across its breadth. An exception to this arrangement of a thin channel of uniform thickness with a transverse field is the axisymmetrical symmetry of hollow fibre FFF, where a fraction of the fluid flows radially outward through the permeable fibre wall (Jönsson & Carlshaf 1989;Wijnhoven et al 1995;Reschiglian et al 2005). On the other hand, a tubular channel with transverse field is not a suitable design for FFF, as explained by Giddings (2000).…”

Hollow-fiber flow/hyperlayer field-flow fractionation for the size characterization of airborne particle fractions obtained by SPLITT fractionation

“…Hollow-fiber flow field-flow fractionation (HF FlFFF), a variant of FlFFF techniques, was first described in a few papers on separation of spherical latex standard particles [13,14], and recently it has been gaining interest as an efficient separation technique for particles [15,16], proteins [17][18][19], and cells [20,21]. Unlike the conventional FlFFF channel system having a rectangular channel design, HF FlFFF is operated in a cylindrical channel utilizing a hollow-fiber membrane module which is very simple in assembly and disposable.…”