Element-specific examination of volatile halogenated organics in wastewater extracts using GC-ICP-MS

Importance of the Topic

Volatile halogenated organic compounds formed during oxidative wastewater treatment represent a growing concern due to their potential toxicity, persistence, and implications for water reuse. Monochloramination and other disinfection processes can transform naturally occurring halide ions into hazardous disinfection byproducts (DBPs). Rapid, selective detection of these compounds is critical for monitoring treatment efficacy, assessing environmental risk, and guiding regulatory decisions.

Objectives and Overview of the Study

This study aimed to develop and validate an element-specific analytical workflow for detecting volatile brominated and iodinated organics in municipal wastewater extracts. The approach compared untreated and monochloraminated samples to characterize changes in DBP formation and speciation.

Methodology

Sample Collection and Preparation:

• Municipal wastewater collected from distinct geographic locations.
• Split into untreated and monochloraminated aliquots.
• Liquid–liquid extraction using methyl tert-butyl ether (MTBE) following a modified EPA Method 551.1 protocol.
• Extracts concentrated into amber GC vials for analysis.

Calibration:

• Standard solutions of 1-bromo-4-iodobenzene in MTBE at 0, 1, 2, 5, 10, 25, and 100 ng/mL.
• Element-specific response measured for bromine (m/z 79, 81) and iodine (m/z 127).

Instrumentation Used

Gas Chromatography–Inductively Coupled Plasma–Mass Spectrometry (GC-ICP-MS):

• GC: Agilent 7890A with heated transfer line and inlet.
• Column: Agilent HP-5 (30 m × 0.32 mm × 0.25 µm).
• Oven Program: 37 °C (6 min), ramp 10 °C/min to 260 °C, hold 11 min.
• Injection: Pulsed splitless (10 psi to 0.75 min, then 5.8 psi).
• ICP-MS: Agilent 7700x in No-gas mode, RF power 700 W, Ar dilution gas 0.4 L/min, 3.0 mm sample depth.
• Mass monitoring: m/z 79, 81 for Br; m/z 127 for I; 0.15 s integration time.

Main Results and Discussion

Retention and Detection:

• 1-Bromo-4-iodobenzene eluted at 20.5 min, with consistent Br and I signals above 5 ng/mL.
• Iodine detected in all non-zero standards; bromine response linear across target range.

Effect of Monochloramination:

• Total volatile organohalogen levels increased upon treatment.
• Marked rise in volatile iodinated DBPs compared to untreated extracts.
• Some native volatile halogenated organics remained resistant to transformation, while others were consumed or converted into new halogenated species.

Element-specific advantages of GC-ICP-MS enabled interference-free, high-sensitivity quantitation of halogen content, surpassing conventional GC-ECD and GC-MS approaches.

Benefits and Practical Applications of the Method

This workflow offers:

• High sensitivity and selectivity for Br and I detection.
• Element-specific quantitation in complex matrices without molecular fragmentation biases.
• Rapid screening of a broad range of unidentified volatile halogenated compounds.
• Applicability for monitoring disinfection processes and guiding treatment optimization.

Future Trends and Potential Applications

Advancements may include:

• Integration with high-resolution GC-QToF for molecular identification of screened DBPs.
• Exploration of alternative treatment strategies to minimize formation of brominated and iodinated byproducts.
• Extension to other emerging halogenated contaminants and real-time monitoring platforms.

Conclusion

The combination of GC-ICP-MS provides a powerful, element-specific tool for profiling volatile halogenated DBPs in wastewater. Monochloramination significantly alters DBP concentrations and speciation, particularly increasing iodinated byproducts. This approach supports improved risk assessment and treatment design for water reuse applications.

References

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