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- Thermal field-flow fractionation (2)
- Asymmetrical flow field-flow fractionation (1)
- Colloids (1)
- Hofmeister series (1)
- Interfaces (1)
- Ion effects (1)
- Soret coefficient (1)
- Specific ion effects (1)
- Thermophoresis (1)
We discuss the effect of electrolytes on retention of aqueous colloidal polystyrene particles in asymmetrical flow (AF-FFF) and thermal field-flow fractionation (ThFFF). In both FFF subtechniques, interparticle interaction leads to non-ideal fractionation behavior, which can result in a sample load dependency. Electrostatic repulsion is reduced with increasing electrolyte concentration, resulting in a pronounced increase of retention. At higher salinities, hydrophobic interactions dominate, thus applications of AF-FFF under physiological conditions are limited. In ThFFF, also the separation mechanism of thermophoresis is affected by ionic shielding and experimental data are in accordance with recent theoretical models of thermophoresis.
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.