Use of integral Doppler anemometry in field-flow fractionation

Abstract

Integral Doppler anemometry (IDA) is applied in analytical field-flow fractionation (FFF) of particles by registering the transverse concentration profiles of particle mixtures in FFF channels. Several applications of IDA in FFF are considered. First, its use in FFF systems with a linear focusing force is discussed, for two qualitatively different schemes: (a) a conventional FFF scheme with a single probe injection; and (b) a laterally non-equilibrium, time-independent scheme with a steady-state particle concentration at the channel inlet. In the conventional scheme IDA allows direct and precise measurements of the equilibrium focusing positions of fractions and, if necessary, the registration of the usual elution curve. In the stationary non-equilibrium regime it allows the analysis time and channel length to be decreased considerably compared with the conventional FFF regime. Second, the possibility of IDA measurements of the lateral field geometry and intensity inside FFF channels by registering the characteristic trajectories of test particles is shown theoretically and experimentally. The specially developed kinematic formalism valid in the case of large transverse Peclet numbers, i.e., for strong enough fields and/or large enough particles, is used. It allows the time-dependent concentration distribution of particles in a flat channel flow with a lateral force applied (FFF conditions) to be obtained analytically for arbitrary profiles of velocity and force immediately following the probe injection.