Effect of spatial confinement on Pb measurements in soil by femtosecond laser-induced breakdown spectroscopy

This study investigates the spatial confinement effect on Pb measurements in soil by femtosecond laser-induced breakdown spectroscopy (fs-LIBS). Spatial confinement within a cylindrical cavity significantly enhanced the intensities of the Pb plasma emission spectrum and the enhancement increased with decreasing diameter of the cylindrical cavity. When the cavity diameter was increased from 3 to 6 mm, the spectral emission enhancement was more delayed and the spatial confinement effect was weakened. The limit of detection (LOD), coefficient of determination (R²), relative standard deviation (RSD), and root mean squared error of cross-validation (RMSECV) were 8.85 ± 0.16 mg/kg, 98.34%, 4.98%, and 0.45%, respectively in the 3 mm diameter cavity and 33.16 ± 1.45 mg/kg, 97.66%, 8.21%, and 0.54%, respectively, in the unconfined measurements. The cylindrical cavity improved the detection sensitivity (as evidenced by the LODs) and the detection accuracy (as evidenced by the RMSECV and RSD values) of fs-LIBS. Overall, the spatial confinement method promises to improve the analytical figures of merit of the fs-LIBS technology.