Single channel chromatographic separation

FFF is a single-phase chromatographic-type separation technique, where separation is achieved within a very thin channel, against which a perpendicular force field is applied. One of the most common forms of FFF is asymmetrical flow FFF (AF4), where the field is generated by a cross-flow applied perpendicularly to the channel. The flow and sample are confined within a channel, consisting of two plates separated by a spacer, which is typically 100-500 pm thick. The upper channel plate is impermeable, while the bottom channel plate is made of a permeable porous frit material. A membrane covers the bottom plate to prevent the sample from penetrating the channel. 

FFF is a one-phase chromatographic system in which an external field or gradient replaces the stationary phase. The applied field can be of any type that interacts with the sample components and causes them to move perpendicular to the flow direction in the open channel. The most highly developed of the various FFF subtechniques is sedimentation FFF (SdFFF), in which the separations of suspended particles are performed with a single, continuously flowing mobile phase in a very thin, open channel under the influence of an external centrifugal force field. 

Chromatographic monoliths are a specific type of chromatographic stationary phase. In contrast to conventional, particle shaped supports, they consist of a single piece of porous material. The pores form a highly interconnected network of open channels through which the mobile phase flows. Therefore, the main transport mechanism of the molecules to be separated is convection. Because of this, mass exchange between the mobile and stationary phase is very fast, similar to that in the membrane supports. In contrast to the membranes, however, monoUths can be prepared in various shapes and dimensions. Besides convective transport, monoliths also exhibit several other unique features ... 

Fieid—Fiow Fractionation. Field-flow fractionation (FFF) employs a one-phase chromatographic system (251,252). Commercial instrumentation is available from Postnova Analytics and Tecan. Separation occurs in a thin channel containing a single moving fluid. The field applied across the channel may be selected on the basis of the solute. Possible fields include sedimentation, cross-flow, concentration, dielectric, thermal, and magnetic. A book (253) and a review (254) of this technique and its comparison with GPC for the characterization of polymer molecular weights have been published. 

---