Proficiency test on the determination of polyethylene and polybutylene terephthalate cyclic oligomers in a food simulant

The outcome of a proficiency test (PT) organised by the European Union Reference Laboratory for Food Contact Materials (EURL-FCM) is presented. The PT was set up to assess the analytical performance of National Reference Laboratories (NRLs) and Official Control Laboratories (OCLs) in the determination of mass fractions of polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) cyclic dimers and trimers in the official food simulant D1 containing ethanol and water (50:50 v/v). The EURL-FCM had developed and validated an analytical method based on HPLC-UV to monitor the homogeneity and stability of the target oligomers in the PT test items and to determine the respective assigned values, as prescribed in ISO 17043, 2010ISO 17043, 2010. The standard operating procedure of the method was provided to the participants and could be used instead of their own routine methods. Laboratory results were rated using z, z' and ζ scores in accordance with ISO 13528, 2015. The standard deviation for proficiency assessment, σ(pt), was set to 20 % of the respective assigned value, for all the four studied oligomers, based on the perception of experts. A total of 36 participants from 26 countries have registered to the exercise. They received two test items. Solution 1 consisted of food simulant D1 fortified with a known mass fraction of the four oligomers, while Solution 2 was obtained by a migration experiment with PET bottles and food simulant D1 and further fortification of the resulting solution with the four oligomers. The majority of the participating laboratories presented satisfactory results for the four PET and PBT oligomers. For the analysis of Solution 1, 79–88 % of the participants obtained |z (or z')-scores| below 2, while the satisfactory performances ranged from 71 to 85 % for Solution 2. This PT has been organised for the first time at EU level for the analysis of polyester oligomers and confirms that most of the NRLs are able to monitor properly these oligomers in the frame of Regulation (EU) No 10/2011.