Flow field-flow fractionation: Critical overview

This overview regards some critical issues in performing flow field-flow fractionation (flow FFF, FlFFF, AF4, HF-FlFFF, HF5). It includes the channel thickness, void time, channel-flow parabolic profile, channel-flow velocity gradient, uniformity of the cross-flow, sample injection time, relaxation/focusing time, width of sample starting zone, retention level, theoretical and experimental zone broadening, hydrodynamic threshold immobilisation/re-mobilisation, sample loss and adsorption, membrane fouling, sample mass overloading, problems with symmetrical channels, non-spherical sample particles, and method development. Good method development practice (GMDP) and good fractogram practice (GFP) is suggested.

► The parameter retention level is suggested to be generally used.
► The void time and the retention level are suggested to be included in fractograms.
► Graphs of cross-flow gradient and channel-flow velocity gradient are suggested to be generally included in fractograms.
► Relaxation/focusing time should not be excessive.
► Hydrodynamic threshold immobilisation/re-mobilisation is hypothesised.