Determination of N-Nitrosamines by USEPA Method 521 using Triple Quadrupole Gas Chromatography Mass Spectrometry

Significance of N-Nitrosamine Analysis

N-nitrosamines are potent carcinogens that can form as disinfection byproducts in drinking water. Monitoring these compounds at sub-nanogram per liter levels is critical for protecting public health and ensuring regulatory compliance under USEPA standards.

Objectives and Study Overview

This study aimed to streamline the detection and quantitation procedure described in USEPA Method 521 by adopting a triple quadrupole GC-MS/MS platform operating in multiple reaction monitoring (MRM) mode. The goal was to demonstrate that this simplified approach could match or exceed the performance of the existing ion trap-based workflow while maintaining method robustness.

Methodology and Instrumentation

• Instrument: Shimadzu GCMS-TQ8040 triple quadrupole gas chromatograph–mass spectrometer.
• Column: Restek Stabilwax-MS capillary column (30 m × 0.25 mm × 0.25 µm).
• GC Conditions: Constant linear velocity at 40 cm/s; oven ramp from 50 °C (2 min) to 220 °C; splitless 2 µL injection.
• MS Conditions: Electron impact ionization at 70 eV; MRM acquisition with two transitions per analyte; argon as collision gas.
• Calibration: Seven-point external standards (0.5–50 ng/L) in methylene chloride; internal and surrogate standards included.

Main Results and Discussion

• Linearity: Correlation coefficients (R²) above 0.9997 for all seven target nitrosamines over 0.5–50 ng/L.
• Detection Limits: Instrument detection limits between 0.05 and 0.22 ng/L, meeting or surpassing Method 521 requirements.
• Accuracy & Precision: At 2 ng/L and 10 ng/L spike levels, recoveries ranged from 89% to 106% with RSDs under 3%, outperforming ion trap results.
• Surrogate Stability: Surrogate recoveries remained within 80–120% over multiple batches, confirming method ruggedness.

Benefits and Practical Applications

The proposed workflow removes the need for chemical ionization and large-volume injections, reducing technical complexity and maintenance. It delivers enhanced sensitivity and specificity for routine drinking water testing and can be readily implemented in environmental analytical laboratories.

Future Trends and Application Opportunities

Further improvements in triple quadrupole technology and data processing software are expected to lower detection limits and support fully automated analyses. The method framework may be extended to other volatile organic contaminants in water, soil, and industrial effluents.

Conclusion

The simplified GC-MS/MS approach using 70 eV EI and MRM detection on a triple quadrupole system provides equal or superior performance to the traditional ion trap MS/MS configuration of USEPA Method 521, offering a robust alternative for the quantitation of N-nitrosamines in drinking water.

References

• USEPA Method 521: Determination of Nitrosamines in Drinking Water by SPE-GC-MS/MS, 2004.
• Cardona S. et al., Poster: Triple Quadrupole GC-MS for Nitrosamine Analysis; Thermo Scientific NEMC 2015.
• Honnold J. et al., Poster: GC-EI-MS/MS of N-Nitrosamines in Water; Agilent Technologies NEMC 2015.
• USEPA 815-R-15-007: Protocol for the Evaluation of Alternate Test Procedures for Drinking Water Analytes, 2015.