*2.5. Analysis Methods for Each Matrix*

Analytical procedures for low-fat and high-fat matrices were based on the official ES 04613.1 method of the National Institute of Environmental Research (2017) and a modified version of another previous method [13].

For high-fat matrices, a 20.0-μL working solution of 4-n-NP RING-13C6 was added to 3.00 g of infant purée, along with 9.00 mL of acetonitrile. After vortexing the mixture for 1 min, the mixture was centrifuged at 1977× *g* at 0 ◦C for 5 min. The acetonitrile phase mixture was then collected. The mixture was extracted again using 9 mL of acetonitrile, as described above. The acetonitrile phase mixture was obtained and combined with the previously collected acetonitrile. After adding Mega Bond Elut-C18 OH combined with disposable liners to the Visiprep™ SPE Vacuum Manifold, the SPE cartridge was activated with 5.00 mL of both methylene chloride and acetonitrile. From this mixture, 3.00 mL of collected acetonitrile was extracted and poured into the activated cartridge. The analyte

was eluted with 5.00 mL of acetonitrile. The collected elution was completely evaporated using N2 flow, and the residue was redissolved with 0.300 mL of hexane. The procedure described above was used to prepare 3.00 g of olive oil.

For low-fat matrices, a working solution of 10.0 μL of 4-n-NP RING-13C6 was added to 3.00 g of enoki mushroom in a separatory funnel. The mixture was added to 20.0 mL of methylene chloride for liquid–liquid extraction. The separatory funnel was agitated vigorously using a vertical shaker for 20 min. After separating the methylene chloride from the mixture, the collected elution was completely evaporated using N2 flow. The dried residue was redissolved with 0.300 mL of methanol. The procedure described above was used to prepare 3.00 g of 7.00% ethanol solution.
