Low-Level Quantification of NDMA and Non-Targeted Contaminants Screening in Drinking Water Using GC-Orbitrap MS

Importance of the Topic

N-nitrosodimethylamine (NDMA) is a potent carcinogenic nitrosamine emerging in drinking water at trace levels. Regulatory agencies worldwide have established action levels below 10 ng/L due to its tumorigenic potential. Analytical challenges include achieving simultaneous high sensitivity and selectivity against complex matrices to avoid false positives and inaccurate quantification.

Objectives and Study Overview

This study assessed the performance of a high-resolution GC-Orbitrap mass spectrometer for:

• Low-level quantification of NDMA in drinking water down to sub-ng/L concentrations
• Non-targeted screening for additional contaminants within a single full-scan analysis

Methodology and Used Instrumentation

Samples were prepared by spiking NDMA standards (0.1–100 µg/L) and deuterated internal standards (d6-NDMA, d14-NDPA) in dichloromethane, followed by SPE extraction of water samples at 0.96–9.6 ng/L. Chromatographic separation was achieved using fast GC (11 min run time). Instrumentation included:

• Thermo Scientific Exactive GC Orbitrap mass spectrometer operated at 60 000 resolving power (FWHM at m/z 200)
• Electron ionization at 70 eV in full-scan mode
• TraceFinder software for quantitative and non-targeted workflows

Main Results and Discussion

• The instrument detection limit for NDMA was 0.09 µg/L (equivalent to 0.1 ng/L in water), with repeatability (%RSD) <9% for NDMA and <6% for d6-NDMA across calibration points.
• Linearity was excellent across 0.1–50 µg/L (R² >0.999) with residuals <9%.
• Mass accuracy for NDMA m/z 74.04747 remained below 1 ppm at both low and high concentrations.
• Surrogate recoveries complied with EPA Method 521 criteria (70–130%).
• Non-targeted screening detected over 220 additional compounds, predominantly halogenated organics linked to disinfection by-products; tetrachloroethylene was confidently identified via deconvolution and library matching.

Benefits and Practical Applications of the Method

• Single full-scan analysis enables simultaneous targeted quantification and non-targeted screening without extra injections.
• High-throughput GC method reduces analysis time to 11 minutes per sample.
• High resolution and mass accuracy minimize matrix interferences and false positives.
• Robust quantification supports regulatory compliance and routine laboratory use.

Future Trends and Potential Applications

• Expansion of high-resolution GC-MS methods to other trace-level emerging contaminants.
• Integration with advanced data processing and AI-driven workflows for comprehensive non-targeted analyses.
• Development of standardized libraries for disinfection by-product screening.
• Application in real-time monitoring and on-site water quality assessment.

Conclusion

The Exactive GC Orbitrap MS platform delivers exceptional sensitivity, selectivity, and mass accuracy for trace NDMA quantification and broad-spectrum screening in drinking water. This unified approach enhances confidence in regulatory compliance and enables detection of emerging contaminants within a streamlined workflow.

Reference

1. Mitch WA, Sharp JO, et al. N-nitrosodimethylamine (NDMA) as a drinking water contaminant: A review. Environ Eng Sci. 2003;20(5):389–404.
2. Sedlak DL, Deeb RA, et al. Sources and fate of nitrosodimethylamine and its precursors in municipal wastewater treatment plants. Water Environ Res. 2005;77(1):32–39.
3. US EPA. Method 521: Determination of Nitrosamines in Drinking Water by SPE and GC 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. App Note 10490. 2015.
5. US EPA. Basic Information about Tetrachloroethylene in Drinking Water. 2014.
6. California DHS. NDMA in California Drinking Water Notification Levels. 2002.
7. Health Canada. Guidelines for Canadian Drinking Water Quality: N-Nitrosodimethylamine. 2011.
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