Analysis of Wastewater Effluent Samples to Identify Toxic Chemicals Using the High-Resolution Agilent 7250 GC/Q-TOF

Significance of the topic

Wastewater effluent can contain diverse toxic chemicals that threaten aquatic ecosystems and water quality. Comprehensive screening is essential to detect both known and unknown contaminants and to understand their contributions to observed toxicity.

Objectives and study overview

This study aimed to develop a broad‐scope suspect screening and nontargeted workflow using a high‐resolution Agilent 7250 GC/Q-TOF to identify toxic compounds in wastewater effluents. It combined targeted analysis of pesticides and environmental pollutants with untargeted discovery and correlated findings with acute toxicity bioassays using Ceriodaphnia dubia.

Methodology

Effluent samples were collected over five days and assessed for mortality in Ceriodaphnia dubia. Samples were filtered and extracted via solid-phase extraction and solvent extraction, spiked with an internal standard, and analyzed by GC/Q-TOF in electron ionization (EI), negative chemical ionization (NCI), and positive chemical ionization (PCI) modes. A 15 m HP-5ms midcolumn backflush configuration with retention time locking ensured reproducible separations. Data were acquired over m/z 50–650 at 5 Hz and processed in Agilent MassHunter Quantitative Analysis 10.1 for suspect screening, and by MassHunter Unknowns Analysis with Agilent Mass Profiler Professional for non-targeted feature finding and statistical comparisons.

Instrumentation used

• Agilent 8890 GC with 15 m HP-5ms multi-mode inlet (cold splitless).
• Agilent 7250 GC/Q-TOF high-resolution mass spectrometer.
• Midcolumn backflush enabled by pneumatic switching device.
• Data processing in MassHunter Quantitative Analysis, Unknowns Analysis, and Mass Profiler Professional.

Key results and discussion

Suspect screening in EI mode identified over 90 pesticides and environmental contaminants per sample with mass errors below 5 ppm and high library match scores. NCI screening detected around 40 halogenated compounds including fipronil and its degradation products. PCA of untargeted data clearly separated samples by toxicity, while volcano plots and correlation analysis highlighted compounds enriched in high-toxicity effluents. Fragment formula annotation confirmed 2,2-dimethoxy-1,2-diphenylethanone, and PCI data enabled identification of acetyl triethyl citrate among candidates correlated with elevated mortality.

Benefits and practical applications

The integrated workflow offers reliable detection across a broad chemical space, links chemical profiles to bioassay outcomes, and reduces false negatives. Retention time locking and backflush strategies enhance reproducibility and instrument longevity. This approach supports environmental monitoring, pollutant source tracking, and risk assessment in regulatory and industrial laboratories.

Future trends and potential applications

Emerging directions include expanded accurate mass libraries, added ionization modes, advanced deconvolution and machine learning algorithms for suspect and nontargeted screening, real-time data processing, and broader use in monitoring emerging contaminants and assessing treatment effectiveness.

Conclusion

High-resolution GC/Q-TOF combined with targeted suspect and nontargeted workflows effectively identifies known and unknown toxicants in wastewater effluents and correlates chemical presence with bioassay toxicity, providing a robust platform for environmental protection and decision support.

References

• SANTE/11945/2015. Guidance document on analytical quality control and method validation procedures for pesticide residues analysis in food and feed.
• FDA, Department of Health and Human Services. Memorandum: Acceptance Criteria for Confirmation of Identity of Chemical Residues using Exact Mass Data within the Office of Foods and Veterinary Medicine (2015).
• Kim S. et al. PubChem 2019 Update: Improved Access to Chemical Data. Nucleic Acids Res. 2019;47(D1):D1102-1109.