Field-flow fractionation of nano- and microparticles in rotating coiled columns

Abstract

Field-flow fractionation (FFF) is a very powerful and versatile set of liquid chromatography-like elution methods. However, conventional FFF separations occur in thin channels and the sample weight injected is usually less than 1mg to avoid overloading. The fractionation in a rotating coiled column (RCC), which can be attributed to sedimentation FFF, enables the handling sample weight to be increased at least up to 1g. An uneven distribution of particles in RCC was first observed by Y. Ito et al. in 1966. The work in this direction was continued by P.S. Fedotov et al. in 2000. Regularities of the behaviour of nano- and microparticles of different size and origin in RCCs with different design parameters were systematically studied taking as example silica particles, latex beads, quartz sand, clay minerals, and other samples. The basic principles of the new FFF method were established. The developed method was applied to the speciation analysis of polydisperse environmental samples, in particular, for the separation of soils into silt, clay and sand fractions. For the first time, nano- and submicron particles of street dust have been separated, weighted, characterized by electronic microscopy, and quantitatively analyzed by ICP-MS (after digestion). The elements that may be of anthropogenic origin (Zn, Cr, Ni, Cu, Cd, Sn, Pb) were found to concentrate mainly in <0.3 and 0.3–1μm fractions. It has been shown that the concentrations of Cr, Ni, Zn in the finest fraction (<0.3μm) of street dust can be one order of magnitude higher than the concentrations of elements in bulk sample. The fractionation in RCC was also used for the recovery of a nearly monodisperse fraction (4.5μm) of a chromatographic sorbent based on polystyrene-divinylbenzene; impurities remaining from the synthesis and smaller particles (1–2μm) being removed. Study on the fractionation of synthetic samples has demonstrated the applicability of the method to the preparative separation and purification of polydisperse materials.