Ion Effects in Field‐Flow Fractionation of Aqueous Colloidal Polystyrene

Abstract

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.

Impact of Ionic Strength of Carrier Liquid on Recovery in Flow Field-Flow Fractionation

“…By increasing the ionic strength their diameter was approximately 694.4 nm, which was almost double the value declared. Similar effect was observed by Lang et al [ 26 ]. They investigated influence of increased NaCl concentrations on retention shift of 25 and 50 nm polystyrene NPs in AF4.…”

“…These ones have a direct effect on the electric double layer (EDL) (Fig. 1 ) of micro sized and nanoparticles [ 13 – 15 ].…”

ICP-MS for the analysis at the nanoscale – a tutorial review

“…Also in case of different cations, elution time effects were observed. 148 Both effects were in accordance with the lyotropic series. As observed by Schachermeyer et al different cations also influence relative recovery (Cs + < K + < Na + ) of nanoparticles such as polystyrene.…”

“…Furthermore, it needs to be kept in mind, that, ICP-MS detection delivers a mass-based information that needs to be converted into a number-based concentration. This can be accomplished based on particle size information obtained either from the AF4 theory (although membrane swelling may decreases the channel height) 148 or from the retention time using calibration with certified particle size standards (refer to Table 1). However, as will be discussed in the following section, the influence of the carrier solution, membrane type and nanoparticle characteristics can result in a shift of the retention time, as reported for Au and SiO 2 nanoparticles under identical AF4 conditions 149 as well as for polystyrene and Ag nanoparticles 150 , which results in erroneous size information.…”

“…As a result a pronounced increase of retention and hydrophobic sample membrane interactions dominate. 148 In case of attractive electrostatic forces agglomerates/aggregates may occur, which may precipitate on the membrane. Two kinds of particle membrane adsorption phenomena are reported: (i) reversible adsorption, leading to peak broadening and peak asymmetry; (ii) irreversible adsorption on the membrane, leading to reduced recovery as e.g.…”