Fully automated sample preparation and analysis of NDMA in potable water using GC-QqQ

Importance of the Topic

Automated detection of NDMA in drinking water is critical due to its classification as a probable human carcinogen and its formation as a disinfection byproduct. Regulatory limits are increasingly stringent worldwide, demanding sensitive, reliable, and high-throughput analytical methods.

Objectives and Overview of the Study

The primary goal was to develop a fully automated workflow for the preparation and analysis of NDMA in potable water, leveraging electron ionization and triple quadrupole GC–MS to meet detection and quantification requirements down to 1 ng/L as per regulatory guidelines.

Used Instrumentation

• Agilent 7890A gas chromatograph coupled with Agilent 7000B triple quadrupole MS (EI source)
• GERSTEL MPS 2 XL-xt autosampler with headspace syringe and SPE needle
• CIS 4 PTV inlet with Universal Peltier Cooling
• ITSP Hardware kit and Coconut Charcoal ITSP SPE cartridges

Methodology

• Solid phase extraction of 10 mL water samples using coconut charcoal cartridges, automated conditioning, equilibration, and elution (×25 enrichment)
• Large volume injection (10 µL) via PTV inlet in solvent vent mode
• GC separation on a DB-WAX column with helium as carrier gas and a two-stage oven program
• Multiple reaction monitoring (MRM) in EI mode with NDMA-d6 as internal standard
• Seven-point calibration in dichloromethane and methanol covering 0.006–0.375 ng/mL and 0.25–15 ng/L in water matrices

Main Results and Discussion

• Linearity with correlation coefficients (R²) of 0.999 and calibration accuracies between 94.6–104.0% (solvent) and 95.5–103.3% (water extracts)
• Absolute recoveries of 63–84% across LC-MS water, tap, and river water; relative recoveries 98–115% with internal standard correction
• Precision: RSD 2.7–4.3% for solvent standards and 7.2–10.7% for spiked water samples
• Instrument detection level (IDL): 0.25 pg on column; method detection limits (MDL): 0.13 ng/L (LC-MS), 0.39 ng/L (tap), 0.30 ng/L (river)
• EI source temperature (150–350 °C) and ionization energy (10–80 eV) variations showed negligible impact on sensitivity

Benefits and Practical Applications

Automation streamlines sample handling, reduces contamination risks, and enhances throughput, making the approach suitable for routine monitoring of NDMA in drinking water facilities to ensure regulatory compliance and protect public health.

Future Trends and Potential Uses

• Extension to additional N-nitrosamines within a single automated workflow
• Interlaboratory comparisons to further validate robustness
• Adaptation for real-time monitoring and integration with advanced data analytics

Conclusion

The fully automated GC–EI-MS/MS method achieves sensitive, accurate, and high-throughput determination of NDMA in various water matrices. Compliance with strict regulatory limits is demonstrated, and the workflow offers a scalable platform for future expansion to other trace-level disinfection byproducts.

References

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• WHO. Guidelines for Drinking-Water Quality, 4th ed.; 2011.
• US EPA. Drinking Water Contaminant Candidate List 3; 2009.
• CDPH. NDMA notification level; 2010.
• Ontario MOE. NDMA MAC in drinking water; 2008.
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• US EPA. Method 521: Trace analysis of N-nitrosamines; 2004.
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