Influence of Operating Parameters On the Retention of Chromatographic Particles By Thermal Field-Flow Fractionation

Abstract

We have investigated the retention behavior of chromatographic particles in thermal field-flow fractionation (FFF). Retention time is found to increase with increasing temperature drop across the channel thickness, as expected for species exhibiting a thermophoretic mobility. Experiments have been performed with a vertically oriented channel rather than by using the classical horizontal configuration as this leads to much more reproducible retention data. In acetonitrile, silica-based particles are more retained than octadecyl-bonded silica particles, which confirms our previous finding, by means of a different method, that the thermophoretic mobility of the latter is smaller than that of the former. Whatever the type of particles and the nature of the carrier liquid, the relative retention time is observed to decrease with increasing carrier flow rate. This indicates that a hydrodynamic lift force acts on particles to move them away from the accumulation wall, as is usually observed in all FFF experiments with micrometer-sized particles. However, upward and downward flow directions in the vertical channel lead to similar retention data, indicating that inertial lift forces have a minor influence on retention. In addition, the relative retention time steadily decreases with increasing sample concentration, suggesting that the hydrodynamic lift force increases significantly with sample concentration. Accordingly, we speculate that a new transport phenomenon, called shear-induced hydrodynamic diffusion, not previously accounted for in the modeling of retention in FFF, is controlling the migration of the particles in the FFF channel. Implications of the influence of this phenomenon in other FFF experiments are discussed.

Thermal Field-Flow Fractionation and Gas Chromatography−Mass Spectrometry in Determination of Decomposition Products of Expandable Polystyrene after Reactions in Pressurized Hot Water and Supercritical Water

“…ThFFF is particularly well-suited for the characterization of industrial polymers and their deformation processes. It has been applied to the determination of molar mass of poly(ethylene terephthalate) (PET) after different plasma treatment procedures and for the investigation of degradation of high molar mass poly(methyl methacrylate) (PMMA) and natural rubber adhesives exposed to an electron beam at different dosages. , In addition, ThFFF has been used for the determination of shear degradation of macromolecules in diluted solutions during fractionation experiments. , It has been found beneficial in the quality control of industrial polymers involving the analysis of microgels and elastomers ,− and in the characterization of complex industrial copolymers and blends. − ThFFF is also considered a promising technique in the study of certain particulate samples in aqueous and nonaqueous carrier solutions. − …”

Thermal Field-Flow Fractionation of Charged Submicrometer Particles in Aqueous Media

“…Thermal field-flow fractionation (ThFFF) belongs to the FFF family of techniques, where retention occurs as a result of an externally applied thermal gradient, i.e., by thermodiffusion. In the past, ThFFF has been applied to characterization of both dissolved macromolecules and colloidal particles suspended in both aqueous and nonaqueous carriers. − However, extended work has mainly been focused on exploiting the capabilities of ThFFF in macromolecule characterization. Such work has led to significant achievements, proving that the capabilities of ThFFF offer specific advantages over those of size exclusion chromatography (SEC): (i) ThFFF is a so-called “universal” molecular weight calibration technique because, once the calibration function is available, it does not need to be renewed for a specific separation channel calibration; (ii) it is recommended for ultrahigh molecular weight characterization since shear stresses that can degrade the sample are minimized with respect to SEC; (iii) it can be applied under high-temperature conditions for samples that are particularly difficult to dissolve.…”