Comprehensive Profiling of Environmental Contaminants in Surface Water Using High-Resolution GC/Q-TOF

Significance of the Topic

Monitoring organic micropollutants in surface water is essential for assessing environmental quality and public health risk. Many contaminants occur at trace levels and span diverse chemical classes, including volatile and nonpolar compounds better suited to gas chromatography. A comprehensive workflow integrating high-resolution accurate mass GC/Q-TOF supports simultaneous detection of known targets, suspect screening, and nontargeted profiling to capture a broad spectrum of environmental pollutants.

Objectives and Study Overview

This work applies an integrated GC/Q-TOF workflow to surface water samples from the Cache Slough Complex in Northern California. The primary goals are to achieve low-level quantitation of priority pesticides, conduct suspect screening against an accurate mass personal compound database, and perform nontargeted identification of unknown contaminants, thus expanding analytical scope and improving environmental monitoring capabilities.

Methodology

Sample collection was conducted at multiple sites in the Sacramento–San Joaquin River Delta. One-liter water samples were filtered and processed by polymeric SPE cartridges, then eluted with ethyl acetate. Filter material was extracted separately with hexane/acetone followed by solvent exchange. The GC method employed retention time locking to chlorpyrifos-methyl, and a midcolumn backflush to minimize contamination and reduce runtime. Data acquisition combined full-spectrum low-energy and standard EI to reveal both molecular ions and fragment information.

Instrumentation

• Agilent 7890B GC with inert flow path and midcolumn backflush
• Agilent 7250 GC/Q-TOF high-resolution accurate mass spectrometer
• 4 mm MMI inlet in cold splitless mode with retention time lock at 9.143 min
• HP-5ms Ultra Inert columns (15 m, 0.25 mm id, 0.25 µm film)
• Helium carrier gas, run time ~20.75 min, oven ramp to 310 °C
• Electron ionization at 70 eV and low-energy mode at 15 eV; m/z 45–550; 5 spectra/s
• Agilent MassHunter Quantitative Analysis 10.1 and Unknowns Analysis software with PCDL and NIST17.L libraries

Main Results and Discussion

Over 100 pesticides and environmental contaminants were confirmed in water extracts using the targeted and suspect workflow, with herbicides (36%), fungicides (25%), and insecticides (21%) predominant. Geographic comparison across sites revealed both shared and unique pollutants, and filter extracts enriched hydrophobic compounds such as pyrethroids and PAHs. Nontargeted screening added further candidates, and application of accurate mass MS/MS enabled structural elucidation of unknowns, exemplified by identification of a chlorothalonil degradation product, 2,4,5-trichloroisophthalonitrile.

Benefits and Practical Applications

The integrated GC/Q-TOF approach delivers broad contaminant coverage with low detection limits and high confidence in compound identification. Laboratories can streamline environmental surveillance by combining quantitation, suspect screening against custom libraries, and nontargeted discovery in a single analysis, supporting regulatory compliance and risk assessment.

Future Trends and Applications

Advances in high-resolution HRMS, expanded accurate mass libraries, and improved in-silico fragmentation prediction are expected to enhance real-time environmental monitoring. Integration of machine learning for feature prioritization and cloud-based data sharing will further accelerate identification of emerging contaminants and support large-scale ecological assessments.

Conclusion

A comprehensive GC/Q-TOF workflow effectively profiles a wide range of environmental pollutants in surface water, combining targeted quantitation, suspect screening, and nontargeted identification. The approach provides sensitive detection, reliable compound verification, and enables discovery of unknowns, offering a powerful tool for environmental analysis.

References

1. Geissen V. et al. Emerging Pollutants in the Environment: A Challenge for Water Resource Management. Int. Soil Water Conserv. Res. 2015;3(1):57–65.
2. Agilent Technologies. Agilent SureMass Technical Overview. Publication 5991-8048EN, 2017.
3. SANTE/11945/2015. Guidance on Analytical Quality Control and Method Validation Procedures for Pesticide Residues Analysis in Food and Feed, 2015.
4. FDA. Acceptance Criteria for Confirmation of Identity of Chemical Residues Using Exact Mass Data. Office of Foods and Veterinary Medicine Memorandum, 2015.