Hofmeister effect in thermal field-flow fractionation of colloidal aqueous dispersions

In this study, the retention of colloidal polystyrene beads in aqueous dispersion in thermal field-flow fractionation (ThFFF) is investigated as function of various types and concentrations of electrolytes in the carrier liquid. A specific ion effect is observed and can be interpreted in terms of Hofmeister series. Addition of salt composed of chaotropic anions to the carrier liquid increases particle retention with increasing ionic strength up to several mM. This effect is less pronounced the more kosmotropic the anions are, up to a decrease of retention by increasing concentration of sulphate and citrate. It is demonstrated that the effect of varying cations is minor as compared to the one of anions with this model system.