## 3 Results and Discussion
### Validation of the HPLC Analytical Method Performance
#### 3.2.5 Liquid Chromatography-Mass Spectrometry Analysis Conditions  
[PERSON] et al. [29] employed liquid chromatography-electrospray tandem mass spectrometry to detect trace amounts of explosives (such as TNT and its diamino metabolites, HMX, RDX, etc.) in lake water and tributaries. Electrospray ionization was applied to the diamino metabolites of TNT, and the negative ion mode was used for all explosive compounds. [PERSON] et al. utilized an optimized liquid chromatography quadrupole time-of-flight tandem mass spectrometry (LC-QToF-MS) protocol to detect various organic explosives and propellants (TNT, DNT, NT, and PETN), with ionization occurring simultaneously in both positive and negative ion modes [30]. In the negative ion mode, most nitro-containing substances were observed as molecular ions [M]\({}^{-}\) or deprotonated molecular ions [M-H]\({}^{-}\). [PERSON] et al. used dual-sorbent solid-phase extraction coupled with liquid chromatography-high-resolution accurate mass spectrometry to determine 14 types of organic explosives, including HMX, RDX, NB, TNT, TATP, and TATB [31]. Based on previously established optimal conditions for HPLC and by referencing operational procedures and experiments from the literature [26; 29; 30; 31], the detection of the organic compound HNS and its major degradation products in wastewater was conducted using LC-MS. In this investigation, the research group utilized hydrodynamic cavitation (HC) technology combined with chlorine dioxide oxidation for the degradation of HNS. Wastewater samples for analysis were collected at the start (0 min) and end (180 min) of the reaction process. To verify the feasibility of the HPLC conditions, a gradient elution system using an ammonium acetate solution and acetonitrile in a 45:55 ratio, with a flow rate of 0.5 mL/min, was employed. The mass spectrometry conditions were set to the electrospray negative ion mode. The detection parameters for the HPLC-MS are listed in Table 8, and the results are presented in Figures 7 and 8. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Time (h)** & **0** & **2** & **4** & **6** & **8** & **24** \\ \hline Concentration (mg/L) & 19.98 & 20.05 & 19.87 & 20.19 & 19.93 & 20.21 \\ RDS \% & & & 0.86 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: The stability of HPLC method for HNS analysis. \begin{table}
\begin{tabular}{c c} \hline \hline
**LC Conditions** & **MS Conditions** \\ \hline Chromatograph: Dinonex Ultimate 3000 UHPLC & Mass spectrometer: Thermo Scientific Q Exactive \\ Column: Eclipse Plus C18 100 mm \(\times\) 4.6 mm, 3.5 μm & Ion source: HESI \\ Column temperature: 30 \({}^{\circ}\)C & Sheath gas rate: 30 arb; Auxiliary gas rate: 5 arb \\ Injection volume: 10.0 μm & Spray voltage: negative ion 2.8 kV \\ Mobile phase: A: 5 mM ammonium acetate solution; & Capillary temperature: 320 \({}^{\circ}\)C; \\ B: acetonitrile & Auxiliary temperature: 300 \({}^{\circ}\)C \\ Gradient elution conditions: 45\%A + 55\%B & S-lens: 50\% \\ Flow rate: 0.5 mL/min & Scan mode: Fullms/dd-ms2 top10 \\ Scanning range: First level scanning: resolution 70,000, \\ range 50–600 \(m/z\); & Collision voltage: NCE15, 30, 45 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: LC-MS chromatographic and mass spectrometric conditions. The total ion chromatograms at 0 min and 180 min were analyzed by integrating HPLC and mass spectrometry (MS), as depicted in Figure 7. Peak I, representing the initial substrate HNS, exhibited a decrease in peak area as the reaction progressed, indicating the degradation of HNS. The analytical conditions of this method were suitable for the detection of HNS via high-performance liquid chromatography. Figure 8 presents the mass spectrum of HNS, detected from Peak I. In ESI-MS, HNS ionizes to form a radical anion molecular ion peak [M]\({}^{-}\) at \(m/z\) 450, which generally agrees with previous detections of HNS where a radical anion molecular ion peak [M]\({}^{-}\) was observed at \(m/z\) 449 [26].