Numerical simulation of band-broadening during hydrodynamic relaxation in frit-inlet field-flow fractionation channels.

The frit-inlet technique is a promising implementation of hydrodynamic relaxation of samples in field-flow fractionation (FFF). The optimization of the process is of great importance in order to maximize overall system efficiency. The mechanism of band-broadening that takes place during hydrodynamic relaxation has been examined using a three-dimensional simulation of the flow inside the triangular end-piece of the channel. This is the first time this contribution to band-broadening has been considered and studied. Particle trajectories in the absence of a transverse field were numerically calculated, thereby isolating this effect from the familiar field-driven relaxation effect. As a first step towards an optimization of the system, the influence of the length of frit element was examined. Band-broadening was examined by determining the number of particles passing through the triangular end-piece as a function of transit time for a uniform particle distribution at the injection point. Due to the complexity of the flow patterns within the system, it is concluded that such numerical simulations are necessary for the optimization of the design and operation of this type of channel.