Overcoming the challenge of quantifying aged microplastic by qNMR spectroscopy

Quantitative nuclear magnetic resonance (qNMR) spectroscopy holds strong potential for environmental microplastic analysis, contingent on addressing the challenge of quantifying aged synthetic microplastics. This study evaluated the application of qNMR for quantifying polystyrene (PS), polyvinyl chloride (PVC), and polyethylene terephthalate (PET), aged under UV exposure and elevated temperatures for 24 days. qNMR was combined with scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy to assess morphological, chemical, and molecular-level changes. SEM revealed surface degradation in PS and PVC, with minimal changes in PET, while FTIR showed increased carbonyl indices (CI), indicating oxidation. qNMR analysis demonstrated consistent microplastic signals between aged and pristine materials, with relative quantification errors from 1% to 18%. Calibration curves showed strong linearity (R² > 0.97), with limits of detection (LOD) between 0.87-2.79 μg mL^-1 and limits of quantification (LOQ) between 2.89-9.29 μg mL^-1. Additionally, degradation products in PS and PVC were quantified, providing a detailed assessment of chemical changes during aging, while PET exhibited no significant degradation. These results demonstrate that qNMR enables sensitive, reliable quantification of aged microplastics. Integration of qNMR, SEM, and FTIR offers complementary insights into microplastic aging and supports the development of robust methods for environmental microplastic monitoring.