GC/Q-TOF Workflows for Comprehensive Pesticide Analysis

Importance of the topic

Monitoring pesticides and other emerging contaminants in water bodies is essential for environmental protection and human health. High-resolution GC/Q-TOF workflows offer comprehensive detection capabilities, enabling both targeted quantification of regulated analytes and broader suspect and non-target screening to identify unexpected compounds.

Aims and overview of the study

This work presents three complementary GC/Q-TOF workflows for river water analysis:

• Target quantification using negative chemical ionization (NCI) GC/TOF for validated pesticide measurement.
• Suspect screening with electron ionization (EI) GC/TOF and a pesticides personal compound database and library (PCDL).
• Non-target screening employing MassHunter Unknowns Analysis to reveal additional contaminants.

Methodology

Water samples were collected in duplicate at six locations across Cache Slough before, during and after rain events. Extraction procedures included:

• Solid-phase extraction (SPE) of 1 L water with surrogate spikes, eluate concentration to 0.2 mL.
• Filter extraction by sonication in hexane/acetone, combined extracts reduced to 0.2 mL.
• GC/Q-TOF analysis: 2.5 µL splitless injection on a 30 m × 0.25 mm × 0.25 µm HP-5MS column.
• Oven programs tailored for NCI and EI modes and automated mass calibration between samples.
• Data processing: target quantification in NCI; suspect screening via PCDL and NIST14 library; non-target screening with deconvolution and retention time matching.

Used instrumentation

• Agilent 7890B Gas Chromatograph
• Agilent 7200 Q-TOF Mass Spectrometer
• HP-5MS Capillary Column (30 m × 0.25 mm × 0.25 µm)
• Emission currents: 35 µA (EI), 90 µA (NCI); Methane reagent gas (40%).

Main results and discussion

Target quantification was validated for 21 pesticides, achieving method detection limits from 0.05 to 5 ng/L and recoveries between 47 % and 299 % across water and filter extractions. Fifteen pesticides were detected in multiple samples. Suspect screening identified 41 additional compounds, with 24 confirmed by LC/Q-TOF overlap and 17 uniquely observed by GC/EI-Q-TOF. Non-target analysis flagged 45 compounds, of which 36 were retention-time confirmed, nine matched by spectral library only, and two corroborated by LC/Q-TOF data.

Benefits and practical applications

• Comprehensive coverage of regulated and emerging pollutants in aquatic matrices.
• Accurate quantification for environmental monitoring and regulatory compliance.
• Enhanced discovery of unexpected or trace-level contaminants through suspect and non-target workflows.
• Synergistic use of NCI and EI modes to broaden analyte detection scope.

Future trends and possibilities

Ongoing improvements in high-resolution mass spectrometry hardware and data-processing algorithms will further boost sensitivity and identification confidence. Combining GC/Q-TOF with complementary LC/Q-TOF platforms can expand polarity coverage. Integration of machine learning for non-target data interpretation and growing spectral libraries will streamline suspect screening and reduce false positives.

Conclusion

The three GC/Q-TOF workflows demonstrated here provide a versatile and robust approach to pesticide and contaminant analysis in river water. Target quantification ensures precise monitoring of priority analytes, while suspect and non-target schemes extend analytical reach to unforeseen compounds, supporting comprehensive environmental risk assessment.

References

1. Moschet C.; et al. LC- and GC-QTOF-MS as Complementary Tools for a Comprehensive Micropollutant Analysis in Aquatic Systems. Environ. Sci. Technol. 2017, 51(3), 1553–1561.
2. Moschet C., Anumol T., Wylie P., Young T. GC/Q-TOF workflows for comprehensive pesticide analysis. Agilent Technologies Application Note 5991-9132EN, March 2018.