Common and Distinctive\nRaman Spectral Features for\nthe Identification and Differentiation of Per- and Polyfluoroalkyl\nSubstances

The\nstandard methods for detecting per- and polyfluoroalkyl substances\n(PFAS) are precise and sensitive, but their operational complexity\nand high costs hinder the regular monitoring. Raman spectroscopy offers\na promising complementary approach due to its fingerprinting ability\nfor trace analysis, low operational cost, and fitness for field-deployable\napplications. However, the effective use of Raman spectroscopy requires\na well-established Raman library, which is currently lacking. This\nstudy proposes a simple drop-coating deposition Raman (DCDR) spectroscopy\nmethod to concentrate PFAS and establish a library. We prepared DCDR\nsamples of thirteen linear PFAS with carboxyl or sulfonic groups and\nseven nonfluorinated alkyl acids with similar chemical structures.\nRaman maps were collected using a 532 nm laser and a confocal Raman\nspectrometer. All tested PFAS shared common Raman bands at approximately\n300, 380, and 725 cm<sup>–1</sup>, with varying band-to-band\nintensity ratios depending on their chain lengths, head groups, and\nextents of telomerization. Principal component analysis was performed\non wavenumbers 200–1,000 and 1,100–1,600 cm<sup>–1</sup> to differentiate PFAS with nonfluorinated alkyl acids and PFAS with\nvarious functional groups. To our knowledge, this research created\na novel experiment-based reproducible Raman spectral library for PFAS,\nlaying a foundation for efficient PFAS screening using Raman spectroscopy.