Micro-Thermal Field-Flow Fractionation in the Analysis of Polymers and Particles: A Review

Abstract

The benefits of the miniaturization of thermal field-flow fractionation (TFFF) channel are reviewed in order to demonstrate that high-performance separations can be achieved with a micro-channel of optimized construction working under carefully chosen experimental conditions and operational variables. Micro-TFFF is highly competitive in comparison with size exclusion chromatography (SEC) of macromolecules for molar masses up to approximately one million g/mol. However, the versatility of micro-TFFF is superior to SEC for macromolecules of ultra high molar masses not only because there is not an inherent highest molar mass limit of the macromolecules that can be separated by micro-TFFF in contrast to SEC but also, as proved experimentally, due to the fact that shear degradation of the macromolecular coils, a well-known phenomenon in SEC, does not occur in micro-TFFF. Such mild conditions permit the analysis of macromolecular aggregates, micro-gels, and similar associative structures without any destruction. Moreover, colloidal submicron and micron-sized particles of synthetic, natural, or biological origin can also be separated and characterized by micro-TFFF without any modification of the separation system. The free choice of the carrier liquids affords an another advantage to micro-TFFF. It has been predicted theoretically and proven experimentally that high resolution is achieved more efficiently by increasing the temperature drop across the separation channel than with a decrease in channel thickness. This is due to the fact that the total heat flow between the hot and cold walls is substantially reduced in micro-TFFF. This makes the operation of the micro-TFFF system not only 30 times more economical from the viewpoint of electrical energy consumption but also safer. The experimental implementation and application to polymer and particle analysis confirmed the potential of micro-TFFF.