A Fully Automated Approach to the Analysis of NDMA in Water

Importance of the Topic

N-Nitrosodimethylamine (NDMA) is a potent genotoxic carcinogen that can form during drinking water treatment. Even at low concentrations (sub-40 ng/L), its presence poses serious health risks, driving the need for sensitive, reliable analytical methods.

Objectives and Study Overview

This study demonstrates a fully automated workflow for enriching and quantifying NDMA in water using instrument-top solid-phase extraction (ITSP) with coconut charcoal cartridges coupled to automated GC/MS injection, enhancing throughput and reproducibility.

Methodology

• Sample Preparation: 10 mL water spiked with 0.025 ng/mL NDMA and 0.04 ng/mL NDMA-d6.
• Cartridge Conditioning: 750 µL dichloromethane, 1 mL methanol, then 2 mL water.
• Extraction: Load sample, dry with nitrogen for 15 min to maximize retention.
• Elution: 400 µL dichloromethane into a 2 mL vial.
• Injection: 10 µL large-volume PTV solvent-vent into GC/MS.

Used Instrumentation

• GERSTEL MultiPurpose Sampler MPS 2 XL with ITSP
• GERSTEL Cooled Injection System CIS 4 (Tenax liner)
• Agilent 7890A GC and 5975C inert XL MSD
• Maestro software v1.4.8.14/3.5

Main Results and Discussion

• Calibration: Seven-point curve (0.125–4 ng/mL) yielded R² = 0.996.
• Recovery: NDMA recoveries (IS-corrected) ranged from 107% to 113%, mean 110%.
• Detection Limit: ~0.1 ng/mL on single-quadrupole GC/MS (SIM mode).
• Internal Standard: Uncorrected recoveries ~40%, highlighting the importance of NDMA-d6 correction.

Benefits and Practical Applications

• Fully automated SPE reduces manual errors and cross-contamination.
• High sensitivity and accuracy for trace NDMA monitoring.
• Applicable to routine environmental testing, QA/QC, and regulatory compliance.

Future Trends and Opportunities

• Adoption of GC/MS/MS (e.g., Agilent 7000 series) to lower detection limits and enhance specificity.
• Expansion of automated ITSP methods to other trace organic contaminants.
• Development of multiplex assays for simultaneous nitrosamine profiling.

Conclusion

The automated ITSP-GC/MS method delivers robust, high-throughput analysis of NDMA in water with excellent linearity, recovery, and sub-ng/mL sensitivity. Incorporating MS/MS detection is expected to further enhance specificity and detect lower-level contaminants.

Reference

• Carrier D. A Fully Automated Approach to the Analysis of NDMA in Water. Anatune Ltd. Technical Note AS119, 2015.