Elimination of edge effects in micro-thermal field-flow fractionation channel of low aspect ratio by splitting the carrier liquid flow into the main central stream and the thin stream layers at the side channel walls.

An optimized construction of the separation channel for micro-thermal field-flow fractionation (FFF) was proposed and studied experimentally. The sample is injected in such a manner that its zone moves along the channel only in the main central stream where the flow velocity profile in the plane parallel to the main accumulation wall is practically flat. This central stream is separated from the contact with the side walls of the channel by thin flowing layers of the free carrier liquid. The retained species do not reach the thin liquid streams at the side walls where the flow rate decreases rapidly to achieve zero at the side wall according to the established 3D flow velocity profile. Such a construction of the channel allows one to reduce the aspect ratio (the ratio of the channel breadth b to its thickness w) without increasing the zone broadening. The hydrodynamic splitting of the outlet streams allows one not only to increase the concentration of the detected species but also the determination of the sign of Soret coefficient.