This standard operating procedure (SOP) describes the preparation of commercial infant milk formula samples for the extraction of microplastics (MPs, 1-1000 µm, ISO/TR 21960:2020). Due to the high complexity of the matrix, which contains both macro- and micronutrients (e.g., proteins, carbohydrates, and fats), the SOP is specifically designed to efficiently remove organic matter while preserving the physical integrity of MPs. The resulting samples are suitable for vibrational spectroscopy analyses – particularly µ-Raman spectroscopy – for the chemical identification, enumeration, and size distribution of microplastics particles according to ISO 16094-2:2025. The SOP is aligned with the analytical approach whose accuracy was assessed in Putzu et al., Talanta Open 12 (2025) 100586 (https://doi.org/10.1016/j.talo.2025.100586). “The project 21GRD07 PlasticTrace has received funding from the European Partnership on Metrology, co-financed from the European Union’s Horizon Europe Research and Innovation Programme and by the Participating States.”• Funder name: European Partnership on Metrology• Funder ID: 10.13039/100019599• Grant number: 21GRD07 PlasticTrace