DEVELOPMENT AND VALIDATION OF A MICRO-RAMAN SPECTROSCOPY METHOD FOR SMALL MICROPLASTIC PARTICLES IN INFANT MILK FORMULA

Microplastics (MPs) are emerging contaminants of anthropogenic origin that pose potential risks to human health and the environment, prompting the European Union to promote harmonised analytical strategies. However, the absence of standardised methodologies and certified reference materials still limits data comparability and traceability. In particular, the lack of standardised methods for MPs detection and characterisation in food remains a major challenge in contamination assessment [1]. In this context, the present study focuses on the development and validation of an analytical approach for the identification and counting of small microplastics (SMPs, 5–100 μm) in infant formula using µ-Raman spectroscopy [2]. Secondary polyethylene terephthalate (PET) SMPs were provided by the German Federal Institute for Materials Research and Testing (BAM) within the PlasticTrace European project in the form of water-soluble tablets in two different batches (Batch 2 and Batch 3), characterised by different particle numbers (1759 ± 141 and 160 ± 22, respectively) and shape. Cleanroom best practices were implemented to minimise cross-contamination. To ensure the reliability of the results, special attention was given to contamination control throughout the analytical process, including the determination of Reporting Limits (ISO 16094-2:2025) for each polymer type and size range. A random filter sub-sampling model was adopted to guarantee representative coverage of the filtering area (50% of coverage, CV < 12% for both batches). Raman measurement parameters such as laser wavelength, power, and acquisition time were investigated to reduce fluorescence and prevent laser-induced degradation. Polymer identification was achieved through spectral matching (HQI > 50%) to reference and custom-made libraries. Recovery rates (97-105%) and particle size distributions confirmed method robustness. The workflow was further validated on milk samples through an inter-laboratory study involving the National Institute of Metrological Research (INRiM) and the University of Parma, following a harmonised sample preparation protocol [2]. Enzymatic-chemical digestion combined with μ-Raman measurements yielded recovery rates of 82–88% for PET SMPs, including particles as small as 5 μm. These results demonstrate that the proposed analytical strategy effectively isolates and identifies SMPs in complex food matrices, ensuring metrological traceability and contributing to the standardisation of microplastics analysis in food safety assessment. REFERENCES [1] T.V. Duncan, S. Afrin Khan, A.K. Patri, S. Wiggins, Anal. Chem. 96 (2024) 4343-4358. [2] M. Putzu, M. Barbaresi, M. Fadda, A. Sacco, M. Piergiovanni, M. Masino, F. Bianchi, K. Altamann, N. Benismail, L. Coïc, I. Fenoglio, M. Mattarozzi, A.M. Rossi, M. Careri, A. M. Giovannozzi, Talanta Open 12 (2025) 100586.