Determination of Ten Nitrosamines in Drinking Water by Gas Chromatography/Electron Ionization Tandem Mass Spectrometry

Significance of the Topic

N-nitrosamines are potent mutagenic, carcinogenic and teratogenic compounds that can form as disinfection byproducts in treated drinking water. Evidence of N-nitrosodimethylamine (NDMA) in tap water and regulatory limits set by agencies such as the U.S. EPA (1–15 ng/L) highlight the need for highly sensitive and selective analytical methods to monitor trace levels and protect public health.

Objectives and Study Overview

This study aims to develop and validate a rapid, robust gas chromatography/electron ionization tandem mass spectrometry (GC/EI-MS/MS) method for quantifying ten common N-nitrosamines in drinking water. Key goals include optimizing solid-phase extraction (SPE) conditions, establishing chromatographic and mass spectrometric parameters for multiple reaction monitoring (MRM), and assessing method performance in terms of sensitivity, linearity, precision, and recovery.

Methodology

• Sample Preparation
  • Dechlorination: 1 g sodium thiosulfate added to 1 L water sample.
  • SPE Enrichment: Carbon GCB cartridges coupled with coconut charcoal were conditioned, loaded with sample, dried under vacuum, and eluted with dichloromethane.
  • Concentration: Eluate dried over anhydrous sodium sulfate and evaporated to 1 mL under nitrogen.
  • Internal Standard: NDPA-d14 spiked at 20 µg/L in final solutions.

Instrumentation

The final extracts were analyzed on a Shimadzu GCMS-TQ8030 triple quadrupole system.

• Gas Chromatography
  • Column: Stabilwax, 30 m × 0.25 mm × 0.25 µm.
  • Carrier Gas: Helium at 40 cm/s linear velocity.
  • Injection: Splitless mode, 2 µL, injector at 230 °C.
  • Oven Program: 60 °C (2 min) → 140 °C at 8 °C/min (8 min) → 240 °C at 30 °C/min (10 min).
• Mass Spectrometry
  • Ionization: Electron ionization (EI), ion source at 200 °C, interface at 240 °C.
  • Detection: MRM with patented UF scanning and ASSP functions for high-speed, high-sensitivity acquisition.
  • Solvent Cut: 5.5 min; collision-induced dissociation dwell time ≥1 ms.

Main Results and Discussion

• Chromatographic Separation: Baseline resolution achieved for ten N-nitrosamines with retention times from 7.35 to 16.94 min.
• Linearity: Six-point calibration from 1 to 100 µg/L yielded correlation coefficients (R²) of 0.9995–0.9999.
• Sensitivity: Limits of detection below 0.05 ng/L for all analytes.
• Precision: Repeatability tests (n=5) at 0.5 µg/L showed RSD <10%.
• Recovery: Spiked samples at 5 ng/L delivered recoveries of 73.2%–97.6%.

Benefits and Practical Applications

• High sensitivity allows compliance monitoring against regulatory limits in drinking water.
• Rapid SPE extraction and GC/MS/MS analysis streamline routine laboratory workflows.
• MRM and UF scanning ensure selectivity in complex water matrices.

Future Trends and Applications

• Automation of SPE and on-line coupling to GC/MS for higher throughput.
• Application of high-resolution mass spectrometry for non-target screening of nitrosamine precursors.
• Portable MS instruments and sensor technologies for in-field nitrosamine monitoring.
• Integration with machine learning for data processing and trend analysis.

Conclusion

A validated SPE–GC/EI-MS/MS method has been established for ten N-nitrosamines in drinking water, demonstrating excellent sensitivity, precision, and recovery. This approach offers a robust tool for regulatory compliance and water quality assurance.

References

• US EPA Method 521: Determination of Nitrosamines in Drinking Water by SPE and GC/MS.
• Shimadzu Application Note WP-027 (ASMS 2013), Peng Gao et al., “Determination of Ten Nitrosamines in Drinking Water by GC/EI-MS/MS”.