Colloid characterization by sedimentation field-flow fractionation: correction for particle-wall interaction.

The effect of particle-wall interaction on retention ratios in sedimentation field-flow fractionation (FFF) is shown to be describable in terms of a semiempirical parameter δ(w) having units of length. A method of experimentally determining the value of this parameter for a given system is presented. It requires the determination of retention ratios for a set of particle standards over a range of field strengths. The value of δ(w) is simply obtained from the slope of a certain straight line plot of the retention data. Once determined, this parameter may be incorporated into the procedure for the determination of particle diameters from measured retention times to take account of the effects of particle-wall interaction. In principle, δ(w) is independent of field strength and is the same for different FFF instruments providing they employ the same carrier liquid and channel wall material. Therefore, δ(w) values have the potential to be universal system constants transferable from one instrument to another.