Common and Distinctive Raman Spectral Features for the Identification and Differentiation of Per- and Polyfluoroalkyl Substances

The standard methods for detecting per- and polyfluoroalkyl substances (PFAS) are precise and sensitive, but their operational complexity and high costs hinder the regular monitoring. Raman spectroscopy offers a promising complementary approach due to its fingerprinting ability for trace analysis, low operational cost, and fitness for field-deployable applications. However, the effective use of Raman spectroscopy requires a well-established Raman library, which is currently lacking. This study proposes a simple drop-coating deposition Raman (DCDR) spectroscopy method to concentrate PFAS and establish a library. We prepared DCDR samples of thirteen linear PFAS with carboxyl or sulfonic groups and seven nonfluorinated alkyl acids with similar chemical structures. Raman maps were collected using a 532 nm laser and a confocal Raman spectrometer. All tested PFAS shared common Raman bands at approximately 300, 380, and 725 cm –1, with varying band-to-band intensity ratios depending on their chain lengths, head groups, and extents of telomerization. Principal component analysis was performed on wavenumbers 200–1,000 and 1,100–1,600 cm –1 to differentiate PFAS with nonfluorinated alkyl acids and PFAS with various functional groups. To our knowledge, this research created a novel experiment-based reproducible Raman spectral library for PFAS, laying a foundation for efficient PFAS screening using Raman spectroscopy.