Accuracy assessment of a micro-Raman spectroscopy method for small microplastic particles in infant milk formula

The presence of microplastics (MPs) in the food chain is increasingly documented, raising concerns over potential risks to human health. Despite growing efforts, standardized methods for MPs detection in food matrices remain limited. This study presents an interlaboratory comparison (ILC) aimed at assessing the accuracy and comparability of an analytical approach for the identification and quantification of small MPs (5–100 µm) in infant milk powder using µ-Raman spectroscopy and a representative polyethylene terephthalate (PET) reference material (RM). The RM, formulated as water-soluble tablets, was designed to replicate the morphology, size distribution, and polymer composition of environmentally relevant MPs, and was previously assessed for homogeneity and stability for mass fraction and particle numbers. The approach was assessed using two PET RM batches with different MPs particle numbers (high load batch: 1759 ± 141 MPs; low load batch: 160 ± 22 MPs), subjected to an enzymatic–chemical digestion, followed by µ-Raman analysis performed independently in two laboratories with different instruments and operators. Results are reported as absolute particle counts per analyzed sample and demonstrated excellent recovery across all size classes, including the smallest particles (down to 5 µm), with recovery rates ranging from 82 % to 88 %, in good agreement with the RM reference values. The analytical approach proved to be robust, reproducible, and suitable for low-level MPs quantification in complex food matrices, supporting ongoing efforts toward method harmonization and standardization for reliable MPs monitoring in the food sector.