Based on some round robin experiments organized in the last years by a DIN working group and by the IUPAC working party IV.2.2, the paper discusses measures for getting a better interlaboratory reproducibility of GPC results. The most important points are:
‐ selecting columns according to their separation selectivity and range
‐ avoiding artifacts in the distribution curves, caused by gaps in the pore volume distribution
‐ avoiding adsorption and memory effects
‐ calibration: using calibration standards of high quality selecting suitable calibration points checking the influence of the injected concentration
‐ selecting a common detector
‐ data treatment, especially finding the correct baseline
‐ preparing a detailed data report according to a uniform schedule.
This report presents the results from IUPAC Working Party IV.2.2 of the global trial within the framework of IUPAC Commission IV.2, “Characterization of Commercial Polymers”. The results were compared on the basis of molecular weight obtained by size exclusion chromatography (SEC)using different techniques practiced in participating laboratories, the majority of which were materials suppliers. The practical methodologies used different solvents for the polymers, in particular, benzyl alcohol, 1,1,1,3,3,3 hexafluoropropan-2-ol and tetrahydrofuran; the latter solvent was used after chemical modification of the polyamides, in general with trifluoroacetic anhydride. Eight laboratories participated in the trial. The repeatability for molecular weight in each laboratory was good, whatever technique was used, the relative standard deviation averaged over all laboratories being around 3%. The deviations in distribution of molecular weights with different experimental methodologies were broader, but were reasonably good despite the diversity of methods. The differences in the distribution correspond to a confidence interval of about 30% in molecular weight.
Size exclusion chromatography (=SEC) is a widly used method for determining the molecular weight distribution of polymer samples. But using aqueous elution solvents, this method is even today combined with numerous problems, mostly caused by the polyelectrolyte structure of water soluble polymers. Therefore we will firstly give a survey of this special features and discuss preventive measures. From this view then some working rules will be derived with special regard to the devices, columns and calibration standards available today. Finally we will give some remarks about the specific experimental conditions for ultrahigh molecular weight samples.
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