Test MethodDetermination of molecular weights by size exclusion chromatography (SEC) - Results of round robin tests

Results obtained from two round robin test programmes are summarized and presented. Size exclusion chromatography (SEC) in both organic and aqueous phases was used to determine the average molar masses of six different polymers. The data were collected by Empa and evaluated using a robust statistical method concerning repeatability and reproducibility standard deviations. Refractive index (RI) and light scattering (LS) were utilized for signal detection. The results of the measurements indicate that the determination of molecular weights by LS is associated with a high degree of uncertainty compared to data measured by RI. For the SEC measurements in the aqueous phase, repeatability is good, unlike reproducibility. Comparisons of molar mass data determined by aqueous SEC in different laboratories are regarded as at least doubtful.