Total nitrogen (TN) is a critical indicator of water eutrophication. Conventional detection methods (e.g., alkaline potassium persulfate digestion and the Kjeldahl method) suffer from complex sample preparation, time-consuming operations, and reagent-induced pollution. Laser-induced breakdown spectroscopy (LIBS) offers unique advantages for rapid water quality analysis, yet it predominantly relies on costly actively Q-switched lasers, with passive Q-switching rarely explored due to multi-pulse output instability. This study employed a passively Q-switched laser as the excitation source for water TN measurement. By optimizing the multi-pulse trigger position, the signal-to-background ratio (SBR) was effectively enhanced. Combined with the substrate liquid–solid conversion method, key parameters (trigger delay, laser energy, argon flow rate) were optimized. Laboratory measurements of KNO3 standard solutions (0–25 mg/L) using cyanogen (CN) molecular spectral lines yielded a coefficient of determination (R2) of 0.98, and a limit of detection (LoD) of 2.19 mg/L. Tests on actual water samples showed relative deviations ranging from 3.93% to 6.39%. These results demonstrate that passively Q-switched LIBS is a viable, cost-effective solution for rapid water nitrogen detection.
Chen et al. (Sat,) studied this question.