The European Union Reference Laboratory for Food Contact Materials (EURL‑FCM) organised a proficiency testing round, designated FCM‑23/02, to evaluate the ability of national reference laboratories (NRLs) and official control laboratories (OCLs) to quantify styrene in milk at a concentration that is proposed as the new specific migration limit (SML) of 0.040 mg kg⁻¹ in a forthcoming amendment to Commission Regulation (EU) 10/2011. The test was conducted in accordance with Regulation (EU) 2017/625 on official controls for food and feed, and was open to laboratories across the European Union and Switzerland. Twenty‑seven laboratories registered, and twenty‑six submitted results, comprising 17 NRLs from 19 member states and nine OCLs. The participants were instructed to analyse two test items: a commercial UHT milk (T1) and the same milk spiked with styrene (T2) at the target concentration. The spiked sample was prepared by the EURL‑FCM, and its homogeneity and stability were verified before distribution. The assigned value for T2 was 0.040 mg kg⁻¹, with an associated uncertainty that was propagated from the preparation and analytical steps. The evaluation of the results employed a standard deviation for proficiency assessment (σpt) calculated from the inter‑laboratory spread, and each laboratory’s result was scored against predefined criteria that considered bias, precision, and compliance with the assigned value. The majority of participants achieved scores above the threshold, indicating that they can reliably detect and quantify styrene in milk. The overall performance demonstrated that the analytical methods used—primarily gas chromatography coupled with mass spectrometry—are robust and suitable for routine official control. Minor deviations were observed in a few laboratories, mainly due to differences in sample handling or calibration procedures, but these did not compromise the overall assessment. The questionnaire completed by the participants revealed that most laboratories had established protocols for styrene analysis and that the proficiency test helped identify areas for improvement, such as the need for more stringent quality control of calibration standards.

The collaboration involved a broad network of institutions. The EURL‑FCM, based at the Joint Research Centre, coordinated the entire exercise, from the design of the test items to the distribution of samples, collection of data, and statistical evaluation. National reference laboratories such as the Austrian Agency for Health and Food Safety (AGES), the Belgian Sciensano, the Danish National Food Institute, the French Laboratoire National de Métrologie et d’Essais (LNE), and the German Bundesinstitut für Risikobewertung (BFR) contributed expertise in method development and validation. Official control laboratories from countries including Italy, Spain, Sweden, and Switzerland participated, providing a practical perspective on routine testing. The project was funded under the EU’s framework for food safety and compliance, with the JRC’s Food and Feed Compliance Unit overseeing the administrative aspects. The time frame spanned from the invitation letter issued in early 2023, through sample preparation and distribution in the spring, to the submission of results by late summer and the final report in autumn. This coordinated effort not only assessed current analytical capabilities but also supported the harmonisation of testing procedures ahead of the regulatory change, ensuring that member states can enforce the new styrene migration limit consistently across the internal market.