Polarization-resolved LIBS for chromium quantification in soil: a novel chemometric model for matrix effect suppression and detection limit enhancement

Abstract

The polarization characteristics of element emission lines, influenced by local magnetic fields and atomic transition mechanisms in plasma, offer a promising approach to enhance the accuracy of laser-induced breakdown spectroscopy (LIBS) in complex matrices. To address the interference of soil matrix components in chromium detection and improve the stability of quantitative analysis, a polarization-resolved correction model has been derived based on Fresnel equations and Malus's law. This model establishes the relationship between the polarization state of plasma emissions and the complex refractive index at Brewster angle incidence, and insights have been provided on how laser polarization and angle influence plasma excitation efficiency and emission properties. 150 sets of LIBS and polarization-resolved LIBS (PRLIBS) data were collected by using soil samples spiked with five reference concentrations of Cr. Robust correlations between spectral line intensities and reference concentrations were established through linear fitting analysis, and the stability of spectral recognition was demonstrated. The results indicate that the polarization-corrected model significantly improves the linearity between the emission line intensities and the reference concentrations. Compared to conventional LIBS, the stability of the three characteristic emission peaks of Cr is markedly enhanced. By optimizing spectral line intensities through polarization orientation adjustment, the model effectively suppresses matrix-induced interference signals. This method demonstrates superior feasibility and reliability for in situ soil analysis, providing a powerful tool for accurate detection of heavy metals in environmental monitoring.