New opportunities for the non target analysis of environmental contaminants gas chromatography Orbitrap mass spectrometry

Importance of the topic

Non-target screening of environmental contaminants by high-resolution mass spectrometry enables the discovery of previously unrecognized toxic by-products and emerging pollutants. Iodinated disinfection by-products (iodo-DBPs) and short-chain chlorinated paraffins (SCCPs) can exhibit increased genotoxicity, persistence, and regulatory concern, highlighting the need for sensitive and selective analytical approaches.

Objectives and study overview

This work addresses two main goals:

• To investigate the formation and identification of iodinated disinfection by-products generated during chlorination and chloramination of natural organic matter spiked with bromide and iodide.
• To evaluate the performance of a bench-top Orbitrap GC–MS system for the targeted and non-targeted analysis of SCCPs, focusing on sensitivity, selectivity, linearity, and resolving power in both electron ionization (EI) and negative chemical ionization (NCI) modes.

Methodology and instrumentation

Lab-scale disinfection reactions were performed in Milli-Q water fortified with Nordic reservoir humic material, KBr and KI, using free chlorine or monochloramine. Analytes were retained on XAD resins, eluted with ethyl acetate, and concentrated. SCCP technical mixtures (63 % and 55.5 % chlorine) were prepared in cyclohexane over 1–10 000 pg/μL by serial dilution and spiked with polychlorinated biphenyls to assess selectivity.

The analytical platform comprised a Thermo Scientific Q Exactive GC Orbitrap GC-MS system operated in full-scan at up to 60 000 resolving power. Both EI and NCI (methane reagent gas) modes were used. Data processing utilized Thermo Scientific TraceFinder software for spectral deconvolution, NIST library searching with forward search index, and high-resolution filtering (HRF) to assign elemental compositions at sub-ppm mass accuracy.

Main results and discussion

Key findings include:

• Eight iodo-DBPs were confidently identified, with significantly higher concentrations in chloraminated versus chlorinated samples, demonstrating the system’s capability for non-target discovery.
• Spectral deconvolution coupled with HRF scoring improved confidence in structure assignment beyond simple library match scores.
• In EI mode, instrumental detection limits for SCCP mixtures were approximately 10 pg/μL; NCI enabled limits of quantification as low as 3 pg/μL for individual homologue groups.
• Excellent linearity (R2>0.99) was achieved across 1–10 000 pg/μL for both technical SCCP mixtures in EI and NCI.
• Higher resolving powers (>30 000) were necessary to resolve SCCP congeners from isobaric interferences, particularly in NCI, ensuring accurate quantification.

Benefits and practical applications

The Orbitrap GC–MS workflow provides:

• High selectivity and sub-ppm mass accuracy for confident identification of unknown and regulated compounds.
• Simultaneous capability for non-target screening and targeted quantification across a broad dynamic range.
• Improved data quality for water utilities, regulatory monitoring, QA/QC laboratories, and research in environmental analytical chemistry.

Future trends and potential applications

Advancements may include automated non-target workflows integrated with machine learning, expansion to other classes of emerging contaminants, real-time monitoring capabilities, and coupling with complementary separation techniques. Adoption of high-resolution GC–MS can inform regulatory guidelines and support comprehensive contaminant profiling in complex matrices.

Conclusion

The high-resolution accurate mass Orbitrap GC–MS platform demonstrates robust performance for the discovery and quantification of iodinated disinfection by-products and SCCPs. Its unmatched selectivity, sensitivity, and resolving power facilitate reliable non-target screening and targeted analysis, empowering environmental laboratories to detect emerging hazards with confidence.

References

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3. Postigo C, Cojocariu CI, Richardson SD, Silcock P, Barceló D. Anal Chem. 2016; DOI:10.1007/s00216-016-9794-3.