In this work we highlight the size-independent influence of the material properties of nanoparticles on their retention behavior in asymmetric-flow field-flow fractionation (A4F). The phenomena described here suggest there are limits to the effectiveness and accuracy of using a single type of nanoparticle standard (polystyrene beads most typically) in order to generically calibrate retention time in normal mode elution. The dual objectives of this paper are to (1) demonstrate the uncertainties resulting from current practice and (2) initiate a discussion of these effects and their origins. The results presented here illustrate clearly that the retention time is higher for metallic nanoparticles relative to lower (bulk) density nanoparticles of the same nominal size. By modifying the fundamental field flow fractionation equation to account for differences in particle density, we show that the effect of gravitational forces is finite but insignificantly small for nanoparticles. We postulate that the observed material dependent retention behavior may be attributed to differences in the attractive van der Waals force between the nanoparticles and the accumulation wall (membrane surface). We hope that the work presented here will stimulate discussion and reassessment of the calibration procedure, perhaps by more fully accounting for all influential material parameters relevant to the fractionation of nanoscale particles by A4F.
Citation: Analytical and Bioanalytical Chemistry
Pub Type: Journals
field flow fractionation, nanoparticles