Optimisation of ambient and high temperature asymmetric flow field-flow fractionation with dual/multi-angle light scattering and infrared/refractive index detection.

Asymmetric flow field-flow fractionation (AF4) enables to analyse polymers with very high molar masses under mild conditions in comparison to size exclusion chromatography (SEC). Conventionally, membranes for AF4 are made from cellulose. Recently, a novel ceramic membrane has been developed which can withstand high temperatures above 130 degrees C and chlorinated organic solvents, thus making it possible to characterise semicrystalline polyolefins by HT-AF4. Two ceramic membranes and one cellulose membrane were compared with regard to their quality of molar mass separation and the loss of the polymer material through the pores. Separating polystyrene standards as model compounds at different cross-flow gradients the complex relationship between cross-flow velocity, separation efficiency, the molar mass and peak broadening could be elucidated in detail. Moreover, the dependence of signal quality and reproducibility on sample concentration and mass loading was investigated because the evaluation of the obtained fractograms substantially depends on the signal intensities. Finally, the performance of the whole system was tested at high temperature by separating PE reference materials of high molar mass.