Explicit role of ionic strength in retention behavior of polystyrene latex particles in sedimentation field-flow fractionation: Slip boundary model.

We investigate an explicit role of the ionic strength in the retention behaviors of polystyrene (PS) latex particles in sedimentation field-flow fractionation (SdFFF) by hinging upon the retention theory recently developed [1] asR=(R+v)/(1+v). Here R is an experimental retention ratio, and R is the analytical expression of the standard retention theory based on the parabolic flow velocity. The reduced boundary velocityv is expressed in terms of the ionic strength I of the carrier liquid as v=v/(1+εI), where v=0.070and ε=60 mM for all the PS latex systems under investigation. We then apply this to study the explicit ionic strength effect on the retention behaviors of PS beads of 200, 300, 400, and 500nm, respectively. As a primary result, the strong dependence of the retention ratio on the ionic strength can be quantitatively accounted for in an excellent accuracy: The slip effect at the channel surface is significant, particularly when I≲0.5mM, without showing any distinguishable dependence on the specific additives to control I, such as FL-70, SDS, NaNO, and NaN. Based on the present study, we put forward an experimental means to estimate the ionic strength of an aqueous solution using an FFF technique.