Online Coupling of Field-Flow Fractionation with Raman Microspectroscopy Enables the Advanced Study of Nanoplastics Directly in Food

The detection and understanding of the behavior of nanoplastics (NPLs) in complex (in)organic systems is a growing concern and one of the major challenges in analytical chemistry today. Current analytical methods are limited in terms of sample flexibility and automation, often require laborious pretreatment, and usually only provide limited information about the presence of NPLs without assessing the behavior of the plastics in the matrix. Coupling an asymmetrical flow field-flow fractionation multidetector (AF4-MD) platform with Raman microspectroscopy (RM) represents a significant advancement in the field, offering a novel approach that combines the advantages of a highly flexible, automatable, and informative analytical system (AF4-MD) with a detector able to chemically identify NPLs (RM). Up to now, this pioneering technique has only been used to study different nanoparticles in an aqueous environment. Here, for the first time, we report the application of an AF4-MD-RM platform to detect NPLs in a real unprocessed matrix. The developed approach allowed for the separation, selective detection, and multiparametric characterization of milk components and NPLs (polystyrene, PS beads, 100-500 nm) in a short analytical time without sample pretreatment, while providing PS detection threshold values compatible with those of the currently exploited quantification approaches. These beyond the state-of-the-art results were proved with orthogonal techniques and highlight the game-changing potential of AF4-MD-RM for a straightforward detection of NPLs in complex matrices and the characterization of NPL-matrix interactions.