Practical experience with organic solvent flow field-flow fractionation

Abstract

SummarySeveral types of membrane have been tested for use in organic solvent flow field-flow fractionation in an asymmetric channel. The practical problems most commonly encountered were leakage of air and solvent through the SUpport layer on which the membranes are cast, and Unequal swelling of the membrane and the support layer m the organic solvent, leading to ridging of the membrane in the channel. Three types of membrane Were found suitable for the separation of polystyrene standards with tetrahydrofuran as solvent. The best results were obtained with a fluoropolymer membrane. l~air agreement was found between theory and practice for the dependence of retention times on the relative molecular mass of the standards and on the flow regime. Use of scanning electron microscopy revealed that for a rmmber of the membrane materials some pores were touch larger than expected on the basis of the indicated molecular weight cut-off. Whereas these materials could ~aot be used for the ffactionation of soluble polymers, they could be applied with some success to the separation of solid latex and silica particles. A PTFE membrane could be used for the separation of latexes and silica particles suspended in acetonitrile as carrier liquid. In general, however, the retention times of these Particles were shorter than theoretically predicted.

Hollow-Fiber Flow Field-Flow Fractionation of Synthetic Polymers in Organic Solvents

“…In flat-channel asymmetrical flow FFF, in which the membrane is clamped between two plates, swelling of the support of the membrane can lead to deformation or rupturing of the membrane. 7 A module has been developed to contain the hollow-fiber membrane that was inspired by a setup developed by Jo ¨nsson and Carlshaf 11 but that has the advantage that it is built completely of standard liquid chromatography equipment. All connections to the fiber consist of Teflon and stainless steel, which are resistant to all but the most aggressive solvents.…”

“…In search of a suitable membrane, researchers have made use of cellulose nitrile, , modified cellulose, and polyaramide materials . Wijnhoven et al have tested several other membrane types and summarized the main practical bottlenecks of organic solvent flow FFF. Although it was found that in principle organic solvents can be used, the long-term stability of the membranes was generally quite poor, and adsorption of solutes to the membranes frequently occurred, having an adverse effect on the separation efficiency.…”

“…Moreover, the setup of HF5 is such that there is room for the fiber to expand under the potential influence of the solvent. In flat-channel asymmetrical flow FFF, in which the membrane is clamped between two plates, swelling of the support of the membrane can lead to deformation or rupturing of the membrane …”