Systematic quantitation for microplastics and nanoplastics based on size-fractionated filtration hyphenated to Raman/SERS and slope-matching strategy

The issue of micro/nanoplastics has attracted widespread attention. The accurate quantitation of micro/nanoplastics remains challenging due to their heterogeneous size distributions. Herein, a systematic method was proposed that integrates Raman or surface-enhanced Raman spectroscopy (SERS) hyphenated to size-fractionated filtration (SFF-R/S) and a slope-matching strategy, thereby enhancing quantitative accuracy in spectral data acquisition and data handling. Micro/nanoplastics were categorized into four size fractions (>1 μm, 500 nm-1 μm, 50-500 nm, and <50 nm). Raman spectroscopy was employed to analyze larger particles, while SERS was used for 50-500 nm and sub-50 nm nanoplastics. In SFF-R/S, the spectral interferences between fractions were eliminated, thereby improving the accuracy of spectral intensities. In external quantitation, a slope-matching method was used to improve analytical accuracy by estimating particle size. The relative error was < 10 % for single fraction quantitation and < 5 % for mixtures. This systematic method works well with micro/nanoplastics of different polymers and showed a detection limit lowered to 2 × 10 g·L for polystyrene (PS) nanoplastics. Its practical utility was validated by the analysis of released micro/nanoplastics from disposable PS cups. This work provides information on chemical components, concentrations, and size distribution of micro/nanoplastics mixtures, which advances our understanding of their environmental behavior and physiological effects.