Hollow-fiber flow field-flow fractionation of synthetic polymers in organic solvents

A modified polyacrylonitrile (PAN) hollow-fiber membrane from a commercial source has been applied as the separation channel in flow field-flow fracti onation (FFF). With the PAN membrane fiber, the application range of flow F FF could be extended to synthetic polymers that are soluble in a variety of organic solvents. The PAN membrane was shown to be resistant to hydrophobi c solvents, such as dichloromethane (DCM), tetrahydrofuran (THF), ethyl ace tate, and methyl ethyl ketone (MEK), as was illustrated by the successful f ractionation of different polymer standards in these solvents. The system p erformance was assessed using polystyrene (PS) standards with ethyl acetate as the solvent For a 100 kDa PS standard, the average recovery was 57%, bu t for standards with a molar mass of 400 kDa and higher, 100% recovery was obtained. A linear relationship between peak area and injected mass was fou nd. The run-to-run and fiber-to-fiber repeatability was determined using 10 0- and 400 kDa PS standards. The repeatability appeared to be satisfactory, with relative standard deviations < 2% for the retention times and < 5% fo r the recoveries of the standards. Plate numbers for the 400 kDa standard o n different fibers were in the order of 110. From measurements on the fract ionation of ferritin aggregates, it is concluded that the instrumental band -broadening is negligible. For an accurate determination of diffusion coeff icients and molecular sizes based on retention times, calibration of the ch annel with standards appeared to be necessary. However, It was shown that t he FFF system could be coupled to a multiangle light scattering (MALS) dete ctor, thus providing an alternative on-line method for calibration. Express ions for the maximum obtainable plate number per unit of time have been der ived for a hollow-fiber flow FFF system. It is shown that an increase in th e system performance can be expected from a scaling down of the fiber diame ter.