REPORT ON THE COOPERATIVE DETERMINATION OF MOLECULAR-WEIGHT AVERAGES OF POLYMERS BY SIZE-EXCLUSION CHROMATOGRAPHY .7. A REPORT ON THE FORTHROUND-ROBIN TEST (NO-1)

Molecular weight averages of polystyrene (PS) samples (SRM 706, SRM 70 5a, and PS-1) were determined at 24 laboratories belonging to the sect ion of special study on SEC, using two sets of PS calibration standard s commercially available at Tosoh (TSK) and Showa Denko (Shodex) compa nies. The PS-1 sample was used in the last three round robin tests. Th e sample concentrations, injection volume and other experimental condi tions were prescribed as at the 2nd round robin test. Two calibration curves were constructed using TSK standards and Shodex standards, resp ectively. Molecular weight averages of the three samples calculated us ing the Shodex calibration curve were 3 to 14% higher than those calcu lated using the TSK calibration curve, and the differences between two molecular weight averages calculated using the Shodex and TSK calibra tion curves were significant at the 1% significance level. This means that when the values of the molecular weight averages are reported, th e reporter has to declare which PS calibration standards were employed .