PRACTICAL EXPERIENCE WITH ORGANIC-SOLVENT FLOW FIELD-FLOW FRACTIONATION

Several types of membrane have been tested for use in organic solvent now field-flow fractionation in an asymmetric channel. The practical p roblems most commonly encountered were leakage of air and solvent thro ugh the support layer on which the membranes are cast, and unequal swe lling of the membrane and the support layer in the organic solvent, le ading to ridging of the membrane in the channel. Three types of membra ne were found suitable for the separation of polystyrene standards wit h tetrahydrofuran as solvent. The best results were obtained with a fl uoropolymer membrane. Fair agreement was found between theory and prac tice for the dependence of retention times on the relative molecular m ass of the standards and on the flow regime. Use of scanning electron microscopy revealed that for a number of the membrane materials some p ores were much larger than expected on the basis of the indicated mole cular weight cut-off. Whereas these materials could not be used for th e fractionation of soluble polymers, they could be applied with some s uccess to the separation of solid latex and silica particles. A PTFE m embrane could be used for the separation of latexes and silica particl es suspended in acetonitrile as carrier liquid. In general, however, t he retention times of these particles were shorter than theoretically predicted.