Asymmetric-Flow Field-Flow Fractionation (AF4)
AF4, the most versatile and common type of FFF, employs a flat-channel configuration (see FFF-MALS and FFF Theory for more details, or view FFF-MALS webinars). Flat separation channels are available in a variety of sizes to optimize sample loading (which impacts the detection of trace quantities of aggregates, fragments and other inabundant species) against run time and solvent consumption. Channel sizes even run to the semi-preparative scale which can purify milligram quantities of protein. Channels are available with different wetted materials, from the basic PEEK to all-metal (for organic solvents) and metal-free.
AF4 channels are available with two standard membrane materials, regenerated cellulose and polyether sulfone. If these materials do not suit your
solvents you can even prepare and install your own membranes, using the convenient cut-out template we provide. Membranes typically last through
dozens if not hundreds of injections, then are disposed of and replaced with another inexpensive membrane at the cost of a few dollars and the effort
of a few minutes of cleaning the separation chamber. Compared to the cost of a new SEC channel, FFF supplies are insignificant!
The advantages of Hollow-Fiber FFF (HF5)
HF5 separation utilizes a hollow-fiber cartridge made of polyether sulfone. The principle of operation is very similar to AF4 but now the channel
is 'rolled' in a tube format instead of flat.
HF5 offers separations with very little volume, high sensitivity, and short analysis time, thanks to the very small volume of the cartridge. You
could say that HF5 is the analog of UHPLC, except - like AF4 - there is no stationary phase and no shear.
HF5 is preferred over AF4 for method development, because it takes minimal sample, time and solvent consumption. The Eclipse HF5 channel cartridge
typically serves for more than a hundred injections, then may be replaced by a fresh cartridge within seconds. Downtime is minimized, and there is no
membrane to install or cleaning step required.
Sensitivity is a primary benefit of HF5, which has the highest sensitivity of all Flow-FFF variants. The reason is the low channel volume -
typically below 100 µL - and high crossflow density. Moreover, HF5 has the ideal channel geometry with a completely linear flow path and no depletion wall which supports higher efficiency.
Increase in productivity
HF5 runs on the hollow-fiber are fast and need very little sample amount. The Eclipse DualTec offers disposable HF5 channel cartridges
which can be replaced in seconds at minimal costs. After method development the separation can be transferred for scale-up to AF4 channels which
allow higher sample load.
Which to choose?
Your choice of solvents may limit your system to AF4 operation; conversely, for aqueous systems sample availability may constrain you to working
with HF5. With an Eclipse DualTec, you don't have to choose! You can install both AF4 and HF5, or just one or the other with SEC, and reconfigure as
your needs change.