Retention perturbations due to particle-wall interactions in sedimentation field-flow fractionation

In this paper theoretical and experimental results are obtained relating to the perturbation in retention in sedimentation field-flow fractionation due to particle-wall electrostatic and van der Waals interactions. These perturbations are described in relationship to standard retention theory, an ideal theory whose basic assumptions are summarized. A general equation in integral form is given for retention ratio R, and it is shown how the standard retention theory and sterically corrected retention theory are thereby obtained. Expressions are given for the potential energy of a colloidal particle near a wall resulting from electrostatic and van der Waals interactions; these interactions alter the concentration profile in the field-flow fractionation channel in a way that requires numerical integration to get R. By the use of estimated interaction parameters, R is plotted against field strength and ionic strength for several wall materials including stainless steel and fluorocarbon resin. Experimental results are reported for five different carrier solutions including distilled water. The agreement between theory and experimental results is very good considering the approximate nature of the parameters used. Both the calculations and the measurements show that the retentive perturbations are smaller for fluorocarbon resin than for stainless steel, Hastelloy C, and polyimide surfaces. Anmore » intermediate ionic strength also appears to be optimal. A new separation technique based on the combination of field-flow fractionation and potential barrier chromatography is suggested, and its possible advantages are discussed.« less