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

Significance of the Topic

Volatile halogenated organic compounds formed during oxidative water treatment pose a potential health risk due to their toxicity and persistence.
Accurate and rapid screening of brominated and iodinated disinfection byproducts (DBPs) in wastewater is essential for environmental monitoring and public health protection.

Objectives and Study Overview

This study aimed to develop an element‐specific analytical method using gas chromatography coupled with inductively coupled plasma mass spectrometry (GC-ICP-MS) to detect and quantify volatile halogenated organics in municipal wastewater extracts.
The focus was on comparing untreated wastewater with samples treated by monochloramination to assess changes in concentration and speciation of halogenated DBPs.

Applied Methodology and Instrumentation

Sample Preparation

• Municipal wastewater collected from multiple sites, split into untreated and monochloramine‐treated aliquots.
• Extraction performed with methyl tert-butyl ether following a modified EPA method 551.1 protocol.
• Organic extracts transferred to amber GC vials for analysis.

Instrument Configuration and Conditions

• Gas Chromatograph: Agilent 7890A with heated transfer line and injector, HP-5 column (30 m × 0.32 mm × 0.25 µm), pulsed splitless injection.
• GC Oven Program: 37 °C hold for 6 min, ramp at 10 °C/min to 260 °C, hold 11 min.
• ICP-MS: Agilent 7700x in no gas mode, RF power 700 W, 3 mm sampling depth, Ar dilution gas at 0.4 L/min, monitoring m/z 79, 81, 127 with 0.15 s integration.
• Calibration standards prepared in MTBE using 1-bromo-4-iodobenzene at 0, 1, 2, 5, 10, 25, 100 ng/mL.

Key Results and Discussion

Retention and Sensitivity

• 1-bromo-4-iodobenzene eluted at 20.5 min with clear baseline separation.
• Iodine detected in all standards; bromine signals were linear above 5 ng/mL.

Impact of Monochloramination

• Treated samples showed a marked increase in total volatile halogenated organics.
• Iodinated species exhibited a greater relative rise, indicating preferential formation under chloramine conditions.
• Some halogenated compounds persisted unchanged, suggesting resistance to transformation, while others likely formed new DBPs.

Element‐Specific Insights

• GC-ICP-MS provided interference-free quantification of bromine and iodine content, overcoming limitations of GC-ECD and GC-MS/MS.

Benefits and Practical Applications

The element-specific approach enables rapid screening of unknown halogenated species without extensive molecular fragmentation data.
The high sensitivity and selectivity support reliable monitoring of wastewater treatment efficacy and DBP formation.
This method can be integrated into QA/QC workflows for industrial and municipal water quality laboratories.

Future Trends and Potential Applications

Combining GC-ICP-MS with high-resolution mass spectrometry (e.g., GC-QToF) to identify molecular structures of unknown DBPs.
Adapting the workflow to include other halogens such as fluorine and chlorine for comprehensive profiling.
Investigating treatment process modifications to minimize formation of toxic brominated and iodinated byproducts.
Deploying real-time online monitoring systems based on element‐specific detection for continuous water quality assessment.

Conclusion

An Agilent 7890A GC coupled to a 7700x ICP-MS provides a robust, sensitive, and element‐specific method for analyzing volatile halogenated organics in wastewater.
The technique effectively distinguishes brominated and iodinated DBPs before and after monochloramination, offering valuable insights for treatment optimization and public health protection.

Reference

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