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

Reducing air interference is one of the most important steps in achieving direct determination of 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 air interference in LIBS. The longitudinal spatially resolved spectrum of N I 746.831 nm at different breakdown position was obtained and optimized by imaging the plasma on the spectrometer entrance slit. By selecting the pixel range of plasma from 1-256 to 25-80, the background equivalent concentration (BEC) was reduced from 34.29 ppm to 9.58 ppm. Furthermore, the limit of detection (LoD), R2, the average relative error (REAV), and the root mean square error of cross validation (RMSECV) were improved from 2.01 to 0.53 ppm, 0.7779 to 0.9554, 24.76% to 15.22%, and 11.03 to 3.63 ppm, respectively. The results shown that the weak air interference and higher quantitative analysis performance of plasma amplification LIBS could be obtained by spatially resolved spectroscopy.