HIGH-RESOLUTION POLYMER SEPARATIONS IN A 4-PASS HAIRPIN THERMAL FIELD-FLOW FRACTIONATION COLUMN

A thin-channel four-pass hairpin thermal field-flow fractionation (FFF) column is described, and the advantages of its unique dimensional characteristics are explained. The problem of isolating the performance of this and other separations columns from the ubiquitous polydispersity effects are discussed and treated theoretically. The discussion is extended to sixe exclusion chromatography, and it is shown that the 2 to 6 times lower selectivity of the latter compared to FFF leads to the requirement for 4 to 36 times more theoretical plates to encounter polydispersity effects and thereby obtain information on polymer molecular weight distribution. Various experimental and theoretical attempts are made to isolate the polydispersity and column contributions to plate height, including cut-and-recycle experiments, the observation of plate height versus velocity curves, and the direct calculation of the contributing effects. The various methods are subject to moderate errors, but are in rough agreement. The plate height plots show that the polydispersity effect contributed 53% and 68% to the measured plate height for 51,000 and 160,000 molecular weight samples, respectively.