Analysis of Nine N-Nitrosamines Using Liquid Chromatography - High-Resolution, Accurate-Mass Mass Spectrometry

Importance of the Topic

N-nitrosamines are highly mutagenic and carcinogenic compounds found in water sources, foods, and industrial materials. Effective trace-level monitoring is vital for protecting public health and ensuring regulatory compliance.

Objectives and Study Overview

This work presents a liquid chromatography–high-resolution accurate-mass mass spectrometry (LC-HRAM MS) method to separate, identify, and quantify nine common N-nitrosamines in drinking water and wastewater. The study evaluates sensitivity, precision, accuracy, calibration performance, and extraction efficiency.

Methodology and Instrumentation

Sample Preparation:

• Solid-phase extraction based on US EPA Method 521.
• Internal standards NDMA-d6 and NDPA-d14 added at 20 μg/L before analysis.

Chromatography:

• UHPLC system: Thermo Scientific Dionex UltiMate 3000 RSLC.
• Column: Hypersil GOLD C18 (1.9 μm, 100 × 2.1 mm).
• Mobile phases: water + 0.1% formic acid (A), methanol + 0.1% formic acid (B).
• Flow rate: 500 μL/min; injection volume: 100 μL.

Mass Spectrometry:

• Instrument: Thermo Scientific Q Exactive hybrid quadrupole-Orbitrap.
• Full-scan MS at m/z 50–500, resolving power 70,000, AGC target 1×10^5, max injection time 100 ms.
• Electrospray ionization in positive mode; spray voltage 5.5 kV; capillary temperature 350 °C; sheath gas 75 Arb; auxiliary gas 25 Arb; sweep gas 2 Arb; S-Lens RF level 55%.
• Data acquisition and control via Xcalibur 2.2 SP1 with Dionex DCMSLink 2.12.

Key Results and Discussion

• Chromatographic separation achieved in under 6 minutes with retention times from 0.8 to 4.2 min.
• Mass accuracy within ±3 ppm across all analytes.
• Instrumental detection limits ranged 0.2–12 ng/L; method detection limits in water matrices up to 12 ng/L.
• Calibration linearity over 0.05–100 μg/L with correlation coefficients R² > 0.9939.
• Precision (RSD) ≤19%; accuracy bias ≤8.2% at QC levels.
• Extraction recoveries of 68–83% in drinking and wastewater, outperforming the 52% reported in EPA Method 521.

Benefits and Practical Applications

This LC-HRAM MS approach offers faster analysis compared to traditional GC-MS, with enhanced sensitivity and mass accuracy for trace-level N-nitrosamine monitoring. It is well suited for environmental laboratories, quality assurance, and regulatory surveillance.

Future Trends and Potential Applications

• Automation of solid-phase extraction to boost sample throughput.
• Non-targeted screening of emerging nitrosamine analogues using full-scan HRAM data.
• Integration with online sample preparation and real-time water quality monitoring systems.

Conclusion

The presented LC-HRAM MS method on a Q Exactive Orbitrap demonstrates rapid, reliable quantification of nine N-nitrosamines in water matrices, offering clear advantages over established GC-MS workflows.

Reference

• Ngongang AD, Duy SV, Sauvé S. Analysis of nine N-nitrosamines using liquid chromatography-accurate mass high resolution-mass spectrometry on a Q-Exactive instrument. Anal. Methods. 2015. DOI:10.1039/C4AY02967D.
• US EPA. Method 521: Determination of Nitrosamines in Drinking Water by Solid-Phase Extraction and Capillary Column GC-MS/MS. 2005.