Discovery of emerging disinfection by-products in water using gas chromatography coupled with Orbitrap-based mass spectrometry

Significance of the Topic

Disinfection of drinking water is essential to prevent waterborne diseases but leads to the formation of disinfection by-products (DBPs). Among these, iodinated DBPs pose elevated health risks compared to chlorinated and brominated analogues. Their low concentrations and the complexity of treated water demand advanced analytical techniques for comprehensive identification and characterization.

Objectives and Study Overview

This study aimed to detect and elucidate emerging iodinated DBPs in chlorinated and chloraminated water. By applying gas chromatography coupled to a high-resolution Orbitrap mass spectrometer, the work focused on uncovering both known and novel iodo-DBPs in laboratory-treated natural organic matter solutions fortified with bromide and iodide.

Methodology and Instrumentation

Natural organic matter from a reference reservoir was spiked with 500 ppb bromide and 50 ppb iodide. Lab-scale chlorination and chloramination reactions were performed, followed by extraction on XAD resins and elution with ethyl acetate. Dried extracts were analyzed by GC-Orbitrap MS under the following conditions:

• GC system: TRACE 1310 with TG-5MS column (60 m × 0.25 mm, 0.25 μm film)
• Injection: 1 µL splitless, inlet 280 °C, He carrier at 1.2 mL/min
• Oven program: 40 °C (1 min), ramp 15 °C/min to 325 °C (10 min)
• Mass spectrometer: Q Exactive GC hybrid quadrupole-Orbitrap
• Ionization: EI at 70 eV and CI with methane; ion source 230 °C (EI), 185 °C (CI)
• Full-scan range 50–650 Da, resolving power 60 000 (FWHM at m/z 200), lockmass m/z 207.03235
• Data processed in TraceFinder with spectral deconvolution, NIST library search, high-resolution filtering (±2 ppm) and fold-change analysis

Main Results and Discussion

More than 2 500 peaks were detected in chloraminated extracts. An exact mass filter at m/z 126.90392 isolated iodine-containing features, reducing candidates to 15 major peaks. A combined library match score and high-resolution filter (HRF) facilitated confident annotation. Eight iodo-DBPs were identified and confirmed by EI, CI and authentic standards:

• Iodomethane
• Chloroiodomethane
• Iodoacetaldehyde
• Diiodomethane
• Ethyl iodoacetate
• Ethyl β-iodopropionate
• Chlorodiiodomethane
• Bromodiiodomethane

Chloramination yielded markedly higher DBP levels, with peak areas 8 to 66 times greater than chlorination and up to 145-fold for diiodomethane. The workflow enabled both library-based identification and elemental composition elucidation of unknowns via accurate mass PCI.

Benefits and Practical Applications

The combination of GC-Orbitrap MS and advanced data processing offers rapid, sensitive, and selective detection of trace iodinated DBPs. Sub-ppm mass accuracy ensures unambiguous determination of elemental composition and structural proposals. This approach supports regulatory monitoring and risk assessment of emerging DBPs.

Future Trends and Opportunities

Emerging directions include:

• Expansion of high-resolution MS libraries for halogenated compounds
• Integration of additional soft ionization methods to enhance molecular ion detection
• Automation of workflow for high-throughput screening in water quality laboratories
• Coupling with toxicity assays and non-targeted metabolomics for health risk evaluation
• Application to other emerging DBP classes and diverse water matrices

Conclusion

This work demonstrates that GC coupled with Orbitrap-based MS and a robust data workflow enables comprehensive discovery and confident identification of iodinated DBPs in disinfected waters. The methodology provides critical insights for water quality management and public health protection.

Reference

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