Detection of nitrogen in water by plasma amplification LIBS assisted with spatially resolved spectroscopy

Abstract

Reducing atmospheric nitrogen (N₂) interference is one of the most important steps in achieving direct determination of the nitrogen element in water by laser-induced breakdown spectroscopy (LIBS). In this work, plasma amplification LIBS assisted with spatially resolved spectroscopy was used to reduce this interference. Plasma amplification LIBS refers to a modified technique where laser-induced plasma is enhanced through laser–aerosol interaction in a quartz tube, amplifying the plasma volume to improve nitrogen signal detection. The longitudinal spatially resolved spectrum of N I 746.831 nm at different breakdown positions was obtained and optimized by imaging the plasma on the spectrometer entrance slit. By selecting the longitudinal pixel range of the plasma emission spectrum on the ICCD from 1–256 to 25–80, the background equivalent concentration was reduced from 34.29 ppm to 9.58 ppm. Furthermore, the limit of detection (LOD) was reduced to 0.53 ppm, and the quantitative analysis accuracy improved by 41.88%. The results show that spatially resolved spectroscopy effectively suppresses atmospheric nitrogen (N₂) interference in plasma amplified LIBS.