Chemical characterization of microplastics from biosolids: a comparison of FTIR and O-PTIR microspectroscopy

Chemical characterization is an important step in microplastics (MP) research. It provides specific information about the MPs' polymer types, thereby enhancing our ability to trace their sources and assess their environmental impacts. Recently, a novel technique known as Optical Photothermal Infrared (O‑PTIR) spectroscopy has emerged for MP identification. With its submicron resolution and production of artifact-free spectra compared to other spectroscopy methods, the O-PTIR technique is potentially a highly reliable and practical tool for MP analysis.1,2 The main purpose of this study was to compare the chemical identification of MPs between the conventional µ-FTIR and O-PTIR. We assessed three different biosolid samples: 1) wastewater treatment sludge; 2) compost, and; 3) biofertilizer. To remove organic matter, the samples were subjected to a clean-up procedure that includes Fenton oxidation, cellulase enzyme degradation, density separation, and filtration through an Anodisc filter (0.20 µm). Each sample was treated in three replicates. Chemical characterization was performed using µ-FTIR and O-PTIR, both in reflection mode. We identified six different polymers in the studied samples, PE, PS, PVA, PET, PVC, and PMMA. The MPs' µ-FTIR spectra were closely matched with the O-PTIR spectra (Figure 1). O-PTIR was more suitable than µ-FTIR for the identification of smaller particles since the spatial resolution (500 nm) is much higher than conventional IR microspectroscopy. In conclusion, O-PTIR is a highly promising and easy to use technique for MP characterization research, and it can greatly improve the number of identified particles during screenings. Also see: https://micro2024.sciencesconf.org/559446/document