Low level quantification of NDMA and non-targeted contaminants screening in drinking water using GC Orbitrap mass spectrometry

Significance of the topic

Accurate detection and quantification of N-nitrosodimethylamine (NDMA) in drinking water is critical due to its classification as a potent carcinogen at concentrations as low as 10 ng/L. Traditional GC-MS approaches often face challenges in balancing sensitivity and selectivity, leading to potential interferences and false positives when analyzing complex water matrices.

Study objectives and overview

This work presents a single-injection method using high-resolution accurate-mass GC Orbitrap technology for:

• Targeted quantification of NDMA at sub-nanogram per liter levels.
• Comprehensive non-targeted screening of additional contaminants in drinking water.

Methodology and instrumentation

Instrumentation and key settings:

• GC-MS system: Thermo Scientific Exactive GC Orbitrap with TRACE 1310 GC, TriPlus RSH autosampler and TraceGOLD TG-1701MS column (30 m × 0.25 mm × 0.25 µm).
• Ionization: Electron ionization at 70 eV; full-scan mass range m/z 50–650; resolving power 60 000 FWHM (m/z 200); mass accuracy <0.5 ppm using PFTBA calibration.
• Sample preparation: Solid phase extraction (1000× enrichment) of tap water spiked at 0.96–9.6 ng/L NDMA; d6-NDMA surrogate and d14-NDPA injection standard.
• Calibration: Solvent standards from 0.1 to 100 µg/L NDMA with deuterated internal standards; data processed with Thermo Scientific TraceFinder for both quantitation and automated deconvolution-based compound identification.

Main results and discussion

• Chromatography: 11-minute GC run time; clear peak shape for NDMA at m/z 74.04747; resolution >100 000 at m/z 74 resolved potential isobaric interferences.
• Sensitivity: Instrument detection limit (IDL) of 0.09 µg/L (0.09 ng/L equivalent post-SPE).
• Repeatability: <4.5 % RSD for d6-NDMA (n=35), ~5 % RSD for d14-NDPA (n=14).
• Linearity: Excellent linear response (R2 >0.999) over 0.1–50 µg/L; %RSD of response factors <9 % for NDMA and <6 % for the d6-NDMA surrogate.
• Mass accuracy: Consistently <1 ppm deviation for the NDMA molecular ion in standards and matrix samples.
• Quantification in water: NDMA recoveries of 88–111 % at 0.96–9.6 ng/L; surrogate recoveries within QC limits (70–130 %).
• Non-targeted screening: Identification of 220 additional compounds absent in procedural blank, predominantly halogenated by-products, pharmaceuticals and monoterpenes. Examples include chloroiodomethane and tetrachloroethylene with high library scores (>890) and mass accuracy <0.5 ppm.

Benefits and practical applications

This GC Orbitrap method offers rapid, robust analysis combining trace-level NDMA quantification and broad non-targeted screening in a single injection. High mass resolution and accuracy reduce false positives, making it well suited for routine environmental monitoring, regulatory compliance and QA/QC in water laboratories.

Future trends and applications

• Extension to other nitrosamines and emerging organic contaminants.
• Integration with larger accurate-mass spectral libraries and advanced data workflows for automated identification.
• Application to diverse water matrices such as wastewater and industrial effluents.
• Development of on-line SPE-GC Orbitrap systems for fully automated monitoring.

Conclusion

The Exactive GC Orbitrap platform achieves sub-ng/L detection and quantification of NDMA with outstanding repeatability, linearity and mass accuracy. Its full-scan capability enables simultaneous targeted and non-targeted workflows, providing a powerful tool for comprehensive drinking water analysis.

References

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3. U.S. Environmental Protection Agency. Method 521: Determination of Nitrosamines in Drinking Water by SPE and GC/MS with Large Volume Injection and CI-MS/MS (2004).
4. Thermo Fisher Scientific. Discovery of Emerging Disinfection By-Products in Water Using GC-Orbitrap MS. Application Note 10490 (2015).
5. U.S. EPA. Basic Information about Tetrachloroethylene in Drinking Water (2014).
6. California Department of Health Services. Notification Levels for NDMA in Drinking Water (2002).
7. Health Canada. Guidelines for Canadian Drinking Water Quality: N-Nitrosodimethylamine (2011).
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