The European Union Reference Laboratory for Food Contact Materials (EURL-FCM) organised a proficiency test (PT) to assess the analytical capabilities of the EU National Reference Laboratories (NRLs) and Official Control Laboratories (OCLs) on the "temperature control" during migration tests by article filling at 70 °C for 2 h in food simulant D1 (ethanol 50 %, v/v), with the subsequent determination of the specific migration of 2,5-bis(5-tert-butyl-2-benzoxazolyl)thiophene (cf. FCM No 500 in EU Reg. 10/2011).
A total of 41 laboratories (25 NRLs and 16 OCLs) from 26 different countries reported results for the "temperature control" exercise. Thirty two laboratories (24 NRLs and 8 OCLs) submitted results for the "FCM No 500 quantification".
For "temperature control", participants were requested to implement the learnings of the previous PTs when designing their experimental set up. Some general instructions were provided by the EURL-FCM. The test specimens consisted of a set of five 0.3 L polypropylene cups. Laboratories were requested to monitor the temperature of the food simulant inside one of the test specimens during the contact phase. Participants were requested to provide details of their operating procedure and to report their temperature readouts. The results show that 59 % of the 41 laboratories were able to maintain the temperature of the food simulant inside the tolerance range (70 °C ± 2 °C) during the entire migration contact time. This is a significant improvement compared to the results obtained in 2015. Another evaluation approach was investigated checking whether the mean temperature of the entire experiment falls in the range of 68-72 °C; 85 % of the laboratories performed successfully.
For the "FCM quantification", the EURL-FCM confirmed the test items to be adequately homogeneous and stable. Laboratories had to develop an appropriate analytical method and to provide details. The assigned values of the migration of FCM No 500 were calculated as the robust mean and robust standard deviation of the results reported by the participants. The laboratory performance was expressed in terms of z and zeta scores in accordance with ISO 13528:2015. The outcome of this exercise was satisfactory for 80 % of the laboratories (24 out of 30). The remaining six laboratories had unsatisfactory z scores higher than 3. Although their quantification performance at 5 µg kg-1 level was unsatisfactory, this does not imply that their methods of analysis may be not be suitable for the determination at the legal specific migration limit (SML) of 600 µg kg-1.
Laboratories were requested to estimate and report their measurement uncertainties. Half of them reported reasonable estimates. The EURL-FCM will organise a dedicated training to share best practices on the topic.
The experimental information collected through the questionnaire further confirms the critical factors affecting the migration experiment: (1) covering/sealing the test specimen to reduce solvent losses, (2) reducing the filling time, (3) using calibrated thermometers/dataloggers and (4) avoiding pre-heating of the test specimen prior to the migration experiment.