Frit-inlet asymmetrical flow field-flow fractionation (FI-AFIFFF: A stopless separation technique for macromolecules and nanoparticles

This article gives an overview of a recently developed channel system, frit-inlet asymmetrical flow field-flow fractionation (FI-AFIFFF), which can be applied for the separation of nanoparticles, proteins, and water soluble polymers. A conventional asymmetrical flow FFF channel has been modified into a frit-inlet asymmetrical type by introducing a small inlet frit near the injection point and the system operation of the FI-AFIFFF channel can be made with a great convenience. Since sample components injected into the FI-AFIFFF channel are hydro-dynamically relaxed, sample injection and separation processes proceed without interruption of the migration flow. Therefore in FI-AFIFFF, there is no requirement for a valve operation to switch the direction of the migration flow that is normally achieved during the focusing/relaxation process in a conventional asymmetrical channel. In this report, principles of the hydrodynamic relaxation in FI-AFIFFF channel are described with equations to predict the retention time and to calculate the complicated flow variations in the developed channel. The retention and resolving power of FI-AF1FFF system are demonstrated with standard nanospheres and protreins. An attempt to elucidate the capability of FI-AFIFFF system for the separation and size characterization of nanoparticles is made with a fumed silica particle sample. In FI-AFIFFF, field programming can be easily applied to improve separation speed and resolution for a highly retaining component (very large MW) by using flow circulation method. Programmed FI-AFIFFF separations are demonstrated with polystyrene sulfonate standards and pululans and the dynamic separation range of molecular weight is successfully expanded.