M. Van Bruijnsvoort et al., Hollow-fiber flow field-flow fractionation of synthetic polymers in organic solvents, ANALYT CHEM, 73(19), 2001, pp. 4736-4742
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.