In an article published on June 6, 2018 in the peer-reviewed journal Water Research Catarina Araujo and colleagues from the CICECO – Aveiro Institute of Materials, University of Aveiro, Portugal reviewed current and future applications of Raman spectroscopy for the identification of microplastics. The authors observe that a “realistic risk assessment” requires “representative data on the abundance, size distribution, and chemical composition of microplastics,” and Raman spectroscopy can be “an indispensable tool for the analysis of very small microplastics.” However, this technique has some drawbacks such as “long measurement time and proneness to spectral distortion induced by fluorescence,” which, nonetheless, can be overcome by the “easily available solutions that contribute to faster and better identification of microplastics.” The authors also discuss several “non-conventional Raman techniques” that could be applied in the future for “real-time Raman detection and imaging of microplastics.”
Another technique that can be used to analyze microplastics is the Fourier-transform infrared spectroscopy (FTIR). A whitepaper by Agilent, published in June 2018, discusses “complete characterization and chemical identification of microplastics using mobile FTIR and FTIR imaging technologies.”
From a toxicological perspective, particles smaller than 1.5 µm are the most relevant because they are more likely to penetrate deeper into the body (see, e.g., European Food Safety Authority’s (EFSA) statement on microplastics in food). The size of the smallest particle reported to be measured with micro-Raman spectroscopy is 1 µm (FPF reported). FTIR-based techniques can reliably measure particles sized 10 µm and above; the possibility to go “down to a few µm” is currently “under research.”
Araujo, C., et al. (2018). “Identification of microplastics using Raman spectroscopy: Latest developments and future prospects.” Water Research 142: 426-440.