GC/Q-TOF workflows for comprehensive pesticide analysis

Importance of the topic

Monitoring pesticide residues in surface waters is vital for assessing environmental exposure and protecting public health. High resolution gas chromatography quadrupole time of flight mass spectrometry (GC Q TOF MS) enables simultaneous qualitative screening and quantitative analysis with improved sensitivity and selectivity.

Objectives and study overview

The study presents three complementary GC Q TOF workflows applied to 51 water samples from the Sacramento San Joaquin River Delta collected before during and after rain events:

• Targeted quantification of 21 GC amenable pesticides in negative chemical ionization mode
• Suspect screening of approximately 750 pesticides and related compounds using electron ionization and exact mass library matching
• Nontarget screening by spectral deconvolution and mass spectral library searching

Methodology and instrumentation

Water samples were filtered and subjected to polymeric solid phase extraction. Particle bound analytes were recovered by filter sonication. Extracts were concentrated by solvent evaporation and analyzed by GC Q TOF MS in both NCI and EI modes. Data were processed using Agilent MassHunter Quantitative and Qualitative Analysis workflows.

Instrumentation used

• Agilent 7890B gas chromatograph coupled to 7200B Q TOF mass spectrometer
• Negative chemical ionization with methane for targeted analysis
• Electron ionization for suspect and nontarget screening
• Agilent MassHunter software: Quantitative Analysis Find by Formula Unknowns Analysis

Main results and discussion

The targeted method achieved detection limits below 1 ng/L for 18 of 21 compounds with 16 pesticides detected at concentrations from 0.6 to 33 ng/L. Suspect screening identified 41 additional compounds of which 33 were confirmed with standards. Nontarget deconvolution yielded over 1500 components per extract and tentatively identified 25 pesticides 3 transformation products 6 halogenated organophosphates and various water pollutants.

Benefits and practical applications

These workflows enable comprehensive pesticide profiling by combining robust quantification of priority analytes with broad screening for known and unknown contaminants. High resolution mass data and retention time locking reduce false positives and enhance analytical selectivity and throughput.

Future trends and opportunities

Expanding high resolution spectral libraries and integrating GC Q TOF with LC Q TOF workflows will extend coverage to polar thermally labile compounds. Advances in automated data processing and machine learning driven deconvolution promise faster more reliable nontarget analysis.

Conclusion

GC Q TOF methodologies integrating targeted suspect and nontarget approaches provide a powerful platform for thorough pesticide surveillance in environmental waters supporting improved risk assessment and regulatory monitoring.

References

• Moschet C et al Environmental Sci Technol 2017 51(3):1553–1561
• Moschet C Young TM Anumol T Agilent Technologies Application Note 5991-8459EN 2017
• Chen K Sanderson J Agilent Technologies Application Note 5991-8170EN 2017