Our Py-GC-MS calibration standards are composed of carefully selected polymers representative of environmental micro- and nanoplastic pollution. Each polymer batch is sieved through a 300-mesh screen (<50 µm) to ensure particle size uniformity and homogeneity across aliquots. The polymer-matrix blends are subjected to high-energy vortex mixing for 5 minutes. This step is followed by 4 hours of vertical rotation with a knocking effect to loosen any powder adhering to the container. Finally, the sample is horizontally rolled with a swivel effect for 10 hours to thoroughly homogenize the contents (see figure below). Eight 304 stainless steel beads ranging from Ø = 2.0 mm to 5.5 mm are included throughout all mixing steps to enhance homogenization. All final samples include three Ø = 3.0 mm 316L stainless steel beads employed in the final mixing process.