VELOCITY PROFILES IN THERMAL FIELD-FLOW FRACTIONATION

Exact velocity profiles in thermal field-flow fractionation (FFF) were numerically computed for twelve solvents and forty different combinations of the temperature drop Delta T across the channel and of the cold wall temperature, T-c. An expression with six coefficients relating the nu parameter of a third-degree polynomial velocity profile which approximates the exact profile with Delta T and T-c was derived for each solvent. Under typical experimental conditions, it provides a nearly two orders of magnitude improvement in the accuracy of the prediction of the retention over the equation based on the classical parabolic profile. A procedure is suggested for using this nu vs. Delta T and T-c expression for extracting the basic FFF parameter lambda from retention data.