Interlaboratory test on polymers: determination of antioxidants in polyolefins

Abstract

This report presents results obtained from two interlaboratory tests performed in 2000 and 2002. Up to 13 participants, mainly from industry and research institutes analysed two different antioxidants in four polymer matrices. The measured data were collected by EMPA and evaluated using a robust statistical method. Repeatability ( r) and reproducibility data ( R) were of special interest, as well as the combined uncertainty of measurements ( u c). Samples of non-stabilised polyolefins were homogeneously doped with accurate well-known quantities of Irgaphos 168 and Irganox 1010. Since no generally valid and universal standard methods for the determination of antioxidants in plastics exist, the interlaboratory test participants were permitted to select an analysis technique of their choice. Almost all laboratories determined the antioxidant contents with HPLC after different pre-treatments. As a result, the most precise HPLC methods could be identified and will be described in this article. The relative repeatability of the determinations was between 1.3 and 5.5%, and the relative reproducibility was in-between 12 and 28% for both antioxidants. No matrix or analyte dependence was observed. The combined calculated uncertainty of measurement ( u c) in all laboratories was between 36 and 86%. Therefore analysts in different laboratories have to expect large variations in results when comparing the results of antioxidant analysis on the same polymer.