Improved Analysis of N-Nitrosamines by Atmospheric Pressure Chemical Ionization Liquid

Importance of the Topic

The determination of N-nitrosamines in water is essential due to their carcinogenic nature and formation during water treatment processes. Effective monitoring at low parts-per-billion levels is required for regulatory compliance and environmental safety.

Study Objectives and Overview

The study focused on refining an existing ASTM method (D8456-22) for thirteen N-nitrosamine compounds plus two internal standards. Key objectives included:

• Enhancing sensitivity and reproducibility across different water matrices
• Establishing a rapid, reliable workflow for direct injection LC-MS/MS analysis
• Validating linearity, precision, and accuracy at trace levels

Methodology and Instrumentation

The optimized workflow involved direct injection LC separation followed by APCI-LC-MS/MS detection. Instrumentation and conditions were:

• Liquid chromatography: Shimadzu Nexera system with Shim-pack GIST C18 column (4.6×150 mm, 5 µm)
• Mass spectrometry: Shimadzu LCMS-8060RX operated in APCI positive mode
• Mobile phase: 0.1% formic acid in water and methanol at 0.7 mL/min flow rate
• APCI parameters: interface voltage 5 kV, CID gas pressure 210 kPa, optimized interface temperature and gas flows
• Injection volume: 300 µL, column oven at 40 °C

Main Results and Discussion

Optimization of parameters improved detection for all targets, achieving:

• Linear calibration range of 0.05–10 ppb with correlation coefficients (R²) >0.994
• Limits of quantitation down to 0.05 ppb in high total dissolved solids (TDS) matrices
• Precision expressed as %RSD <10% and accuracy within 84–118%
• Separation of fifteen compounds in under 15 minutes

The method proved robust across reagent water, dechlorinated tap water, and waters containing up to 3000 ppm TDS.

Benefits and Practical Applications

The refined method offers:

• High-throughput screening capability for environmental and drinking water testing
• Minimal sample preparation via direct injection, reducing analysis time and contamination risk
• Reliable quantitation at trace levels to support regulatory monitoring and quality control

Future Trends and Opportunities

Advancements may include:

• Integration with high-resolution mass spectrometry for enhanced compound specificity
• Automated sample handling and data processing for higher throughput
• Expansion to emerging nitrosamine analogues and other waterborne contaminants
• Field-deployable APCI-LC-MS platforms for on-site monitoring

Conclusion

Systematic optimization of APCI-LC-MS/MS parameters enabled rapid, sensitive, and reproducible analysis of multiple N-nitrosamines in various water matrices. The method meets stringent requirements for trace-level detection and supports routine environmental and regulatory testing.

Reference

• Standard Test Method for Determination of Nitrosamines in Water by Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS), ASTM D8456-22, ASTM International, 2022.