Signal-enhancement mechanisms of Al and Pb in kaolinite by discharge-assisted LIBS

Abstract To mitigate the adverse impacts of insufficient emission intensity and poor detection limits in laser-induced breakdown spectroscopy (LIBS) of trace heavy metal elements in mineral samples with complex matrices such as kaolinite, a pulsed high-voltage discharge-assisted LIBS approach was employed. Natural kaolinite samples were ablated using a 355 nm nanosecond laser, while a 2 kV pulsed discharge was applied to reheat the plasma. The plasma enhancement mechanism was investigated using time-resolved spectroscopy. By optimizing both the gate delay and the inter-pulse delay between the laser and discharge, the emission intensities of Pb I and Al I lines were increased by approximately 7–9 times relative to conventional single-pulse LIBS. The plasma electron temperature increased by 20%–40%, and the electron density increased by approximately 30%. The limits of detection (LOD) for trace Pb and Ba were also evaluated. The LOD of Pb decreased from 95.02 ppm to 47.73 ppm, and the LOD of Ba decreased from 24.95 ppm to 15.07 ppm. These findings provide mechanistic insight into discharge-induced plasma reheating and demonstrate a robust route towards sensitive and precise on-site determination of heavy metal elements in geologically complex matrices.