Complementary analysis of pristine, UV-aged and extracted microplastics using single particle ICP-MS and OF2i-Raman spectroscopy

Microplastics are of growing concern due to their ubiquity and potential risks to ecosystems and human health. Their small size, chemical diversity, and coexistence with natural colloids make comprehensive analysis difficult. Here, we evaluate two emerging single particle techniques, single particle inductively coupled plasma-mass spectrometry (SP ICP-MS) and optofluidic force induction coupled with Raman spectroscopy (OF2i-Raman), for their ability to provide complementary information at single microplastic resolution. SP ICP-MS determined carbon mass per particle and enabled detection of degradation-induced trends in size and abundance, while OF2i-Raman identified polymer type and molecular changes via optical trapping and inelastic light scattering. OF2i-Raman is a novel method in the field of microplastic research and was therefore first benchmarked by analysing mixed suspensions of polymethylmethacrylate (PMMA), polystyrene (PS), and polyamide-6 (PA-6), as well as PA-6 in a soil extract to assess selectivity under complex matrix conditions. Subsequently, both techniques were applied in parallel to study the UV-induced degradation of PA-6 and low-density polyethylene (LDPE) as relevant industrial polymers. SP ICP-MS detected longitudinal carbon loss and relative changes in particle sizes and numbers, while OF2i-Raman revealed polymer-specific structural alterations and detected spectral fingerprints even after extended irradiation. Together, SP ICP-MS and OF2i-Raman link elemental mass with molecular identity, providing complementary insights into microplastic degradation. While SP ICP-MS remains confined to controlled laboratory experiments due to its limited selectivity and size range, OF2i-Raman extends the analytical window to complex matrices and mixed polymer systems.