REPORT ON COOPERATIVE DETERMINATION OF MO LECULAR-WEIGHT AVERAGES OF POLYMERS BY SIZE-EXCLUSION CHROMATOGRAPHY .3. ON THE POLYMER STANDARDSFOR CALIBRATION

The weight average molecular weight (M(W)) of polystyrene samples dete rmined in the first round robin test (RR-1) was compared with those in the second round robin test (RR-2) to analyse the difference in polys tyrene standards for calibration. The data were divided into two group s: data determined at laboratories that used the standards obtained by the identical vendor in both RRs (case 1) and those using the standar ds of different vendors for RR-1 and RR-2 (case 2). The RR-1: RR-2 rat ios for M(W) in case 1 were 1.03 similar to 1.04 in average, but the m aximum was 1.17 and the minimum 0.95. By careful adjustment of calibra tion conditions, the RR-1: RR-2 ratios for M(W) were reduced to 1.01 s imilar to 1.03. In case 2, as long as a calibration was constructed by passing through most data points smoothly, there was no distinct diff erence in calculated M(W) among standards from different vendors. The relative standard deviation of these data, obtained carefully as menti oned above, were 3.9%.