Accurate sulfur determination of coal using double-pulse laser-induced breakdown spectroscopy
Sulfur accurate determination plays a vital role in the evaluation of coal quality. In this work, double-pulse laser-induced breakdown (DP-LIBS) in a helium atmosphere was presented and applied in the sulfur concentration quantification of coal. The ablation plasma generated from the sample surface by the first laser (Nd:YAG laser at 1064 nm, 50 mJ per pulse) was re-excited orthogonally by the second laser pulse (Nd:YAG laser at 1064 nm, 120 mJ per pulse). The intensity of sulfur spectral lines has been enhanced with DP-LIBS and the interference from O I 926.6 has been weakened in the helium atmosphere. The calibration curves of S I 921.3 nm, S I 922.8 nm and S I 923.8 nm have been established for 10 coal samples with S concentration ranging from 0.28 wt% to 4.01 wt%. The best result was achieved with R2 = 0.992, LoD = 0.038 wt%, and RMSECV = 0.143 wt%. The overall results adequately demonstrate that DP-LIBS combined with a helium atmosphere has excellent analytical performance for sulfur determination in coal and enormous potential for on-line detection in the coal industry.