A dual-mechanism pretreatment idea for improving the derived Raman spectrum for (micro)plastic analysis

Abstract

ABSTRACT Raman spectroscopy is an effective tool for microplastic analysis, but its performance can be limited by weak signals and surface interference. This study aims to enhance derived Raman spectra through chemical surface treatments. Fresh and biofouled plastic debris samples, including polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET), were treated overnight with various chemical solutions: 30% H2O2, 5% NaOCl, 5% HCl, and a sequential treatment of 5% HCl followed by 5% NaOCl (HCl:NaOCl). Stereo microscope examinations revealed that single-solution treatments removed some stains but left others behind, while complete stain removal was achieved with the HCl:NaOCl treatment. The control samples exhibited a high fluorescence issue, but oxidation pretreatment effectively reduced this, with 5% NaOCl outperforming 30% H2O2. Despite eliminating fluorescence, residual stains still obscured peak signals. In contrast, the sequential HCl:NaOCl treatment removed almost visible stain, resulting in very clean surfaces, minimal background signals, and significantly higher S/N ratios for peak signals. This study demonstrates that dual-mechanism pretreatments – combining acid dissolution and oxidation – are far more effective than single treatments, benefiting applications that require clean plastic samples for subsequent operations.