Size exclusion chromatography molecular-weight resolution

Advances in size-exclusion chromatography, coupled with refractive index, absorption, viscosity, and lightscattering detectors, and MALDI-ToFMS, have made it possible to accurately determine molecular weight distribution (oligomer profiling), even at the relatively low values of polymeric additives (up to about 5000 Da). Advances in column design, e.g. high-resolution PS/DVB columns (> 105 plates m-1) mean that SEC can provide a valuable alternative to conventional HPLC techniques for the separation of small molecules. 

Size exclusion chromatography (SEC) has been used to measure molecular weight (MW) distribution of humic substances (3, 6-9). Coupled with detection methods such as molecular fluorescence spectroscopy and dissolved organic carbon analysis (7), electrochemical detection (9), and atomic emission spectroscopy (5), SEC has been used extensively to study humic-metal complexes. A major disadvantage of SEC is that it does not provide adequate resolution for separating humic materials as they do not appear to be made up of distinct fractions with large differences in MW. 

This entry provides an overview of thermal field-flow fractionation (ThFFF) and its application to polymer and particle analysis. The separation mechanism is described and contrasted with that in size exclusion chromatography (SEC). The two techniques are somewhat complementary. Thus, SEC typically provides superior resolution of low molecular weight (M) polymers (M <100,000 Da), while ThFFF excels in the separation of high-molecular weight polymers (M >100,000 Da), gels, and particles. 

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