Thermal Field-Flow Fractionation Universal Calibration:  Extension for Consideration of Variation of Cold Wall Temperature

The well-known size exclusion chromatography (SEC) universal calibration allows the characterization of a polymer sample using a set of polymer standards of a different polymer family. This is a polymer-transferable calibration method. A more “universal” calibration method has been proposed for thermal field-flow fractionation (ThFFF) where the calibration constants closely describe the ratio of ordinary (molecular) diffusion coefficient D to thermal diffusion coefficient (or, more correctly, thermophoretic mobility) D T. The universal calibration for ThFFF is therefore instrument or system transferable. Systematic experiments have previously been carried out to verify this calibration method for a wide range of conditions. Results showed that the method holds well provided experimental conditions such as sample size and cold wall temperature T c are the same for each system. This paper quantifies the effect of cold wall temperature on polymer retention in ThFFF and on the universal calibration constants for the polystyrene−tetrahydrofuran, poly(methyl methacrylate)−tetrahydrofuran, and polyisoprene−tetrahydrofuran systems, respectively. The universal calibration for ThFFF is thereby extended to account for variation of cold wall temperature. The extended calibration will allow for accurate data retrieval from analyses obtained at any cold wall temperature. It will even allow for accurate information retrieval when cold wall temperature is not held constant during sample elution, such as may occur with a change in coolant flow rate or with a programmed decay of Δ T.