A COOPERATIVE GPC TEST OF A POLYSTYRENE STANDARD AND ITS PRECISION

A cooperative GPC test on a polystyrene sample polymerized radically was carried out by 21 laboratories using identical procedures. The variation of the average molecular weights obtained was studied in detail. The average coefficients of variation (standard deviations divided by mean values) of number average, weight average, and z-average molecular weights are 11.0, 11.3, and 21.1%, respectively. The calculation method, the type of detector and the number of divisions of chromatogram do not affect remarkably the average molecular weights obtained. The average molecular weights obtained by different laboratories using the identical columns show variations greater than 20%. In order to reduce the average coefficients of variation to less than 10%, it is necessary to pay much attention to slight changes of operative conditions such as the resolving power of the column and the flow rate of solvent.