## 4 Conclusions  
The existing HNS LC-MS detection methods exhibit several limitations:  
The conditions for the detection of HNS using high-performance liquid chromatography (HPLC) are not detailed. Detection typically employs a single wavelength, and numerous subsidiary peaks are present. The detection range is limited; accurate measurements are only possible for HNS concentrations between 0.04-0.64 mg/L and 2.00-20.00 mg/L. This range fails to accommodate concentrations of 0.64-2.00 mg/L and those exceeding 20.00 mg/L. The mobile phase for HPLC detection of HNS predominantly consists of  
Figure 8: Mass spectrum of the HNS peak.  
Figure 7: Total ion chromatogram.  
acetonitrile (ACN). Additionally, some methods even require the dilution of HNS standard solutions with acetonitrile instead of ultrapure water. The detection process takes 20 min, undoubtedly increasing the cost of analysis.  
To address the aforementioned deficiencies, this study established a rapid, simple, sensitive, accurate, and cost-effective method for the qualitative and quantitative analysis of HNS using LC-MS. The analysis was conducted using an Ultimate3000 UHPLC system, utilizing an ACCUCORE C30, 2.6 \(\upmu\)m, 150 \(\times\) 4.6 mm chromatography column, and detection was performed by a UV-visible detector. The optimal test conditions for HNS analysis were established, including detection wavelength, mobile phase, flow rate, column temperature, and injection volume:  
The mobile phase consisted of methanol:ultrapure water at a 70:30 ratio, with a flow rate of 0.5 mL/min, a column temperature of 30 \({}^{\circ}\)C, and an injection volume of 10 \(\upmu\)L. Dual-wavelength detection was employed, using 271 nm as the primary testing wavelength and 226 nm as a secondary wavelength, resulting in chromatograms free of extraneous peaks. HNS exhibited a good linear relationship within the concentration range of 0.50-150.00 mg/L, with a linear fit (R\({}^{2}\)) greater than 0.9999. An examination of the method's linearity and precision confirmed its effectiveness, accuracy, simplicity, high sensitivity, and reliable results. The mobile phase used for HPLC detection of HNS predominantly consisted of MeOH. HNS standard solutions could be diluted with ultrapure water. The analysis could be completed in as little as 6-6.5 min, reducing the detection time by nearly 70%, significantly lowering the cost of HNS analysis while maintaining excellent stability and reproducibility. The choice of mobile phase and the reduced retention time also made the HNS detection process more economical and environmentally friendly.  
Based on the established high-performance liquid chromatography (HPLC) conditions for HNS and methodologies from previous studies, the detection conditions for electrospray ionization quadrupole static orbitrap high-resolution mass spectrometry (ESI-Q Orbitrap HRMS) were determined. The LC-MS parameters are suitable for analyzing HNS products and their wastewater within a concentration range of 0.50 to 150.00 mg/L, meeting the needs for practical sample analysis.  
Conceptualization, M.J. and R.J.; methodology, M.J. and J.G.; software, Y.Q.; validation, M.J., R.J. and J.G.; formal analysis, Y.Q.; investigation, J.L.; resources, Z.H. and Y.J.; data curation, Y.J. and Z.L.; writing--original draft preparation, M.J.; writing--review and editing, Y.Q., R.J. and J.L.; visualization, Z.H. and Z.L.; supervision, R.J. and Y.Q.; project administration, Y.Q.; funding acquisition, Y.Q. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key R&D Program of China (Grant No. 2023 YFC3206400).  
Not applicable.  
The data that support the findings of this study are available from the corresponding author upon reasonable request.  
The authors would like to thank the reviewers and editors for their valuable comments.  
The authors declare no conflicts of interest.