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

Importance of the Topic

Identification of toxic chemicals in wastewater effluents is essential for safeguarding downstream ecosystems and ensuring environmental water quality. Comprehensive and non-targeted screening methods extend beyond conventional targeted analyses, providing a broader detection scope to uncover unknown or unexpected pollutants that may pose ecological risks.

Objectives and Study Overview

This study aims to combine targeted and non-targeted screening approaches using high-resolution gas chromatography/quadrupole time-of-flight mass spectrometry (GC/Q-TOF) to identify toxic chemicals in wastewater effluent samples collected over a five-day period. Toxicity towards the freshwater organism Ceriodaphnia dubia was assessed and correlated with chemical profiles to pinpoint candidate toxicants.

Methodology and Instrumentation

• Sample Preparation: Filtration through 0.45 µm GF/F filters; solid-phase extraction on Oasis HLB cartridges; solvent elution with ethyl acetate and methanol; ultrasonic extraction of filters with hexane/acetone; combined extracts spiked with dibromooctafluorobisphenol internal standard.
• Analytical Approach: Screening performed in electron ionization (EI), negative chemical ionization (NCI) and positive chemical ionization (PCI) modes; retention time-locked GC method ensured consistency with an accurate mass pesticide and pollutant library.

Used Instrumentation

• Agilent 8890 Gas Chromatograph equipped with mid-column blackflush and retention time locking.
• Agilent 7250 GC/Q-TOF Mass Spectrometer.

Main Results and Discussion

• Targeted EI screening identified a suite of environmental contaminants using a unique mass spectral library of over 1 000 compounds.
• NCI-based screening of 118 compounds yielded halogenated pollutants and pyrethroids with enhanced sensitivity.
• Causative toxicants such as flurprimidol, paclobutrazol, azoxystrobin and chlorantraniliprole correlated with higher C. dubia mortality, whereas compounds like fipronil appeared in non-toxic samples.
• Non-targeted (Unknowns) analysis with NIST library and Mass Profiler Professional highlighted additional features, including 5-methyl-1H-indole-2-carboxylic acid ethyl ester and 2,2-dimethoxy-1,2-diphenylethanone, potentially linked to observed toxicity.
• Use of PCI supported molecular ion confirmation and formula annotation for unknown library hits.

Benefits and Practical Applications

• The combined targeted/non-targeted GC/Q-TOF workflow enhances detection of both known pesticides and unknown contaminants in complex wastewater matrices.
• Automated data processing streamlines identification, aiding environmental monitoring and risk assessment in regulatory and industrial laboratories.
• High-resolution accurate mass and multiple ionization modes improve confidence in compound identification, critical for toxicological evaluation.

Future Trends and Possibilities

• Expansion of spectral libraries and databases for emerging pollutants to capture a wider chemical space.
• Integration of hyphenated techniques (e.g., GC×GC-Q-TOF) for improved separation and sensitivity.
• Application of machine learning algorithms to enhance feature extraction and suspect screening in complex environmental samples.
• Development of standardized non-targeted workflows for regulatory acceptance and routine monitoring.

Conclusion

The study demonstrates that high-resolution GC/Q-TOF with combined EI, NCI and PCI screening can effectively detect and prioritize toxic chemicals in wastewater effluents. Both targeted and non-targeted analyses are complementary, providing a comprehensive strategy for environmental water quality assessment and pollutant source elucidation.

Reference

ASMS 2019 Poster MP144, Sofia Nieto et al., Agilent Technologies & UC Davis, Analysis of the Wastewater Effluent Samples to Identify Toxic Chemicals Using High-Resolution GC/Q-TOF.