![]() ![]() The inlet streams are generally introduced to each side of a stream splitter placed between, and parallel to, the channel walls. The virtual surfaces are the result of introducing two fluid streams at the channel inlet, the feed suspension stream and a stream of pure fluid, and dividing the fluid between two channel outlets. This so-called transport lamina is constantly replaced with fresh fluid during the fractionation and has none of the disadvantages associated with a physical membrane. The selective transport takes place across a thin fluid lamina which is defined by two virtual surfaces lying between the channel walls. ![]() The advantage of SPLITT fractionation over crossflow filtration is that the binary separation is obtained without the use of a membrane and therefore without all of the associated problems of membrane fouling and consequent flux reduction. In either case, the feed is selectively depleted of some of its components as it passes along the length of the channel. The rate of transverse transport is therefore either a function of the diffusion coefficients of the feed components, or the mobilities of the components under the influence of the applied field. For submicron particles and macromolecules the transverse transport may occur by diffusion, 5, 6 but if particles are larger than around a micron in diameter, so that diffusional transport is negligible, then some type of field must be applied across the channel thickness to induce migration. A division of flow at the channel outlet completes the separation. Differential transport of feed components occurs across the channel thickness either under the influence of an applied field or by diffusion. The feed stream is introduced, using a sheath flow arrangement, adjacent to one wall of a thin channel. 5, 6 The SPLITT fractionation technique has much in common with crossflow filtration. 1 – 4 It is also useful for selectively removing macromolecules or colloidal materials from a suspension of larger particles. Split-flow thin channel fractionation (or SPLITT fractionation) is a separation technique particularly well suited to continuous sorting of micron size particles. It is concluded that SID may contribute to NSC, but that further experiments and mathematical modeling are necessary to more fully explore the phenomenon. The possible mechanisms for NSC are discussed, and experimental results interpreted in terms of shear-induced diffusion (SID) caused by viscous interactions between particles in a sheared flow. Such contamination is known as non-specific crossover (NSC) and refers to the real or apparent migration of non-mobile particles or cells across streamlines with the mobile material. In such cases, it may be critically important to minimize contamination of the labeled cells with non-labeled cells while at the same time maximizing the throughput. For example, immuno-magnetically labeled biological cells may be separated from non-labeled cells with the application of a transverse magnetic field gradient. Some specialized applications involve the separation of the fraction influenced by the transverse field from the fraction that is not. Typical applications have involved isolation of different fractions from a polydisperse sample. Split-flow thin channel (SPLITT) fractionation is a technique for continuous separation of particles or macromolecules in a fluid stream into fractions according to the lateral migration induced by application of a field perpendicular to the direction of flow.
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