Sequential quantification of number and mass of microplastics in municipal wastewater using Fourier-transform infrared spectroscopy and pyrolysis gas chromatography-mass spectrometry

Plastic pollution is a significant environmental concern because microplastics (MPs) accumulate in various ecosystems; therefore, the accurate identification and quantification of MPs in environmental samples is crucial. This study presents a new sequential analytical method that combines Fourier-transform infrared spectroscopy (FTIR) and pyrolysis-gas chromatography/mass spectrometry (Pyr-GC/MS) to characterize and quantify MPs. FTIR with a microscope allows the identification of the polymer type and physical dimensions of MPs, whereas Pyr-GC/MS enables determining the chemical composition of MPs with plastic additives. Pretreated wastewater influent samples spiked with reference MPs were filtered through an Al2O3 disk for FTIR analysis, and the surface contents were collected and subjected to Pyr-GC/MS analysis. The mass of the reference MPs estimated using FTIR were in good agreement but were slightly lower than those obtained using Pyr-GC/MS. This finding supports the notion that the proposed sequential method can be used to determine both the number and the mass of MPs in environmental samples.