Quantitative analysis of microplastics in water by Raman spectroscopy: influence of microplastic concentration on Raman scattering intensities

<title>Abstract</title> In this study, quantitative Raman scattering analysis was employed for the direct detection of microplastics in water. Raman intensities varied according to the change in the concentration of microplastics in water. Microplastic samples consisted of 40–100 μm polyvinyl chloride (PVC) spherical particles; 40–48 μm polyethylene (PE) spherical particles; 0.1–1.0 wt% of each microplastic sample was dispersed in de-ionized water. In the case of PE particles in water, a peak corresponding to the twisting of the CH₂ bond was observed at 1295 cm^-1, and the area integrated intensity ratio with a H₂O broad peak at 3,400 cm^-1 was observed. The peak area ratio increased linearly with the PE particle concentration, and the linear equation and R² value were y = 0.22797x+0.0125 and 0.92, respectively. In the case of the PVC particles in water, the peak belonging to the stretching vibration of the C–Cl bond appeared at 637 cm^-1, which linearly increased in intensity when the peak area ratio with H₂O was observed. The linear expression and R² value were y = 0.37704x-0.01821 and 0.88, respectively. The results confirmed that the dispersed microplastic particles of PE and PVC in water (up to ~0.1 wt%, and up to 0.22 μm particles) can be directly detected by the Raman scattering analysis method.