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

Significance of Topic

Ensuring safe reuse of wastewater and desalinated sources is critical as freshwater scarcity intensifies. During oxidative disinfection, halide ions like chloride, bromide and iodide form reactive species that generate halogenated DBPs, some of which are toxic at low levels. Particularly, brominated and iodinated DBPs pose greater health risks than their chlorinated analogs. Routine monitoring methods lack element specificity, hindering comprehensive characterization of unknown volatile halogenated organics in wastewater. Element-specific analysis via GC-ICP-MS offers a solution to accurately detect and quantify these emerging contaminants.

Objectives and Study Overview

This study aims to develop and apply a gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP-MS) approach to examine volatile halogenated organics in wastewater extracts before and after monochloramine treatment. Key goals include:

• Evaluating the speciation and concentration changes of brominated and iodinated compounds induced by chloramination.
• Demonstrating element-specific detection capabilities for broad screening of volatile halogenated DBPs.

Methodology and Instrumentation

• Sample Collection and Preparation: Municipal wastewater samples were collected from multiple locations. Each sample was split: one portion untreated, the other treated with aqueous monochloramine. 35 mL aliquots were extracted with 5 mL methyl tert-butyl ether (MTBE) following a modified EPA Method 551.1. Organic layers were transferred to amber GC vials.
• Gas Chromatography: An Agilent 7890A GC equipped with a heated transfer line and injector was utilized. Separation occurred on a 30 m HP-5 column (0.32 mm × 0.25 µm). The inlet operated at 200 °C; transfer line at 260 °C. Injection used pulsed splitless mode (10 psi for 0.75 min, then 5.8 psi). The oven was held at 37 °C for 6 min, ramped at 10 °C/min to 260 °C, and held for 11 min.
• ICP-MS Detection: An Agilent 7700x ICP-MS ran in no-gas mode with 700 W RF power, 0.4 L/min Ar dilution gas and 3.0 mm sample depth. Ions at m/z 79 & 81 (bromine) and 127 (iodine) were monitored with 0.15 s integration. Calibration standards (0–100 ng/mL) were prepared using 1-bromo-4-iodobenzene in MTBE.

Main Results and Discussion

Analyses revealed volatile halogenated organics present in untreated wastewaters, with distinct peaks for brominated and iodinated species. Monochloramination significantly altered speciation: total volatile organohalogens increased, notably iodinated DBPs, and some preexisting compounds resisted transformation while others were consumed. Element-specific detection enabled clear differentiation of Br- and I-containing molecules without molecular interferences. Sensitivity permitted detection of species above 5 ng/mL, with a representative compound eluting at 20.5 min.

Benefits and Practical Application

• Element Specificity: GC-ICP-MS selectively detects halogen elements, reducing interferences and increasing confidence in analyte identification.
• Sensitivity and Screening: The method screens a wide range of unknown organohalogens in a single run, surpassing capabilities of GC-ECD or GC-MS/MS in halogen quantitation.
• Water Quality Management: Rapid assessment of halogenated DBPs supports optimization of disinfection processes to minimize harmful byproduct formation.

Future Trends and Opportunities

Future work will integrate high-resolution GC-QToF to structurally identify unknown halogenated DBPs detected by ICP-MS. Additionally, exploring advanced oxidation or alternative disinfectants could reduce formation of toxic brominated and iodinated byproducts. Coupling elemental screening with non-targeted molecular analyses promises a comprehensive strategy for safeguarding reclaimed water.

Conclusion

The developed GC-ICP-MS method provides an element-specific, sensitive platform for evaluating volatile halogenated organics in wastewater. Monochloramine treatment was shown to enhance formation of brominated and iodinated DBPs, underlining the need for targeted monitoring. The approach offers a valuable tool for water quality researchers and regulators to assess and manage emerging disinfection byproducts.

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