SEC Analysis of Polymers with Light Scattering Detection

Size exclusion chromatography (SEC, also called GPC or GFC) is the most important test method for the determination of the molecular properties of synthetic and natural macromolecules in solution. Different from traditional methods which only establish average property values, SEC allows the simple and fast determination of property distributions of macromolecules, e.g. molecular weight distribution, structure distribution, end group distribution or branching distribution [1]. SEC is often calibrated with reference materials in order to obtain molecular weight distributions and to validate instruments and analytical methods. However, to obtain more extensive structure information (branching, density, etc) or to abstain from a calibration, the use of light scattering detectors for SEC is necessary [2]. Thus, the molecular weight can be measured continuously during elution. Depending on the type of LS instrument used, various qualitative and quantitative properties can be determined: Radius of gyration (Rg) Degree of branching (long chain branching) Molecular structure changes Aggregation/agglomeration behaviour Aging/storage processes. A comparison of the results between conventional SEC and light scattering measurements can show differences, especially when the standards used in conventional SEC and the samples differ. An example is shown in table 1, caused by the unequal hydrodynamic volume of gluten and pullulan molecules. Here the results from conventional SEC with narrow standards can be used only for the comparison of different samples. This is not the case, when using light scattering measurements, where absolute M-values are obtained. Basic Measuring Principles