Leveraging Cl-H Mass Defect Plots for the Identification of Halogenated Organic Contaminants

Significance of the Topic

Time-of-flight mass spectrometry coupled with halogen mass defect analysis offers a robust approach for non-target screening and identification of halogenated organic contaminants in complex environmental matrices. The distinctive mass defects and isotope patterns of chlorine and bromine enable selective filtering of spectral data to isolate compounds of interest.

Objectives and Study Overview

The study aimed to apply Cl-H mass defect plots in conjunction with high resolution TOFMS to detect and tentatively identify known and previously unreported halogenated contaminants in pooled Lake Ontario eel samples. By leveraging accurate mass data and library comparisons, the work sought to expand knowledge of legacy pollutants and emerging compounds in aquatic biota.

Methodology and Instrumentation

• Sample Preparation: Ten Anguilla rostrata specimens collected from eastern Lake Ontario (2008) were homogenized and pooled.
• Extraction and Cleanup: Dichloromethane extraction, 1:1 DCM:hexane partitioning, and gel permeation chromatography.
• Chromatographic Separation and Detection: One microliter injections on a LECO Pegasus GC-HRT system with Agilent 7693 autosampler and 7890 GC using Restek Rxi-guard and Rxi-5MS columns; oven ramp from 90 °C to 320 °C; electron ionization at 36 eV; m/z range 35–850; acquisition rate 6 spectra/s.
• Data Processing: ChromaTOF-HRT software for peak finding, spectral deconvolution, and generation of Cl-H mass defect plots with a mass accuracy threshold of <2 ppm and isotopic spacing criteria for chlorine and bromine.

Key Findings and Discussion

A variety of legacy halogenated contaminants including polychlorinated biphenyls, polybrominated diphenyl ethers, polychlorinated diphenyl ethers, hexachlorobenzene, dieldrin, mirex, and pesticides were tentatively identified. Breakdown products such as DDE, DDD, and a methoxynonachlorodiphenyl ether analogue were also detected. An unexpected finding was fenclorim, an herbicide safener, confirmed via accurate mass and library matching. Cl-H mass defect plots effectively separated halogenated species from siloxane and hydrocarbon background, facilitating targeted screening.

Benefits and Practical Applications

• Efficient filtering of complex datasets to highlight halogenated compounds.
• Non-targeted screening enables detection of both known and unknown species.
• Reduction of false positives through mass defect and isotopic pattern criteria.
• Potential for environmental fingerprinting and comparative studies across matrices.

Future Trends and Applications

Ongoing developments may integrate automated mass defect analysis with machine learning for rapid profiling of halogenated pollutants. Expansion to other heteroatom mass defects and coupling with ion mobility or tandem MS could enhance compound identification confidence. Broader application across environmental and food safety sectors is anticipated.

Conclusion

Cl-H mass defect plotting combined with high resolution TOFMS provides a powerful screening tool for comprehensive non-target analysis of halogenated contaminants. The approach successfully identified a wide range of legacy pollutants and novel species in Lake Ontario eels, demonstrating its value for environmental monitoring and pollution source profiling.

References

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