EPA Method 557 Quantitation of Haloacetic Acids, Bromate, and Dalapon in Drinking Water Using Ion Chromatography and Tandem Mass Spectrometry

Importance of the Topic

Disinfection of drinking water is critical to control microbial contamination but generates by-products such as haloacetic acids (HAAs), bromate and residual pesticides (e.g., dalapon) that pose long-term health risks. Regulatory agencies like the U.S. EPA set maximum contaminant levels (MCLs) for a subset of HAAs (HAA5) at 0.060 mg/L. Reliable, sensitive and rapid analytical methods are needed to monitor these contaminants at trace levels in complex water matrices without extensive sample preparation.

Objectives and Study Overview

This work describes the implementation and performance of EPA Method 557, which couples reagent-free ion chromatography (IC) with tandem mass spectrometry (MS/MS) for direct quantitation of nine HAAs, bromate and dalapon in drinking water. The study aims to demonstrate a simplified workflow featuring direct injection, automated matrix diversion and high-throughput detection, all within a single IC-MS/MS run.

Methodology and Used Instrumentation

Water samples preserved with 100 mg/L NH4Cl are directly injected without extraction, derivatization or concentration. An electrolytically generated hydroxide gradient separates analytes on a Dionex IonPac AS24 column with an AG24 guard, while an ASRS-300 suppressor converts the eluent to water and removes cations. A divert valve routes common inorganic anions (chloride, sulfate, nitrate, bicarbonate) to waste, protecting the MS source. Key instrumental components include:

• Thermo Scientific Dionex ICS-5000 Reagent-Free IC system
• Dionex IonPac AG24 guard and AS24 analytical columns
• Thermo Scientific Anion Self-Regenerating Suppressor (ASRS-300)
• Thermo Scientific TSQ Endura triple quadrupole MS with heated electrospray probe (H-ESI-II)
• Thermo Scientific TraceFinder software v3.2 for data acquisition and processing

Main Results and Discussion

The method achieved baseline separation of all nine HAAs plus bromate and dalapon within a 37-minute run. Calibration in both deionized water and a laboratory synthetic sample matrix (LSSM) fortified at 20 ppb exhibited excellent linearity from 0.25 ppb to 20 ppb (R²>0.995). Method detection limits (MDLs) ranged from 0.021 ppb (DBAA) to 0.214 ppb (DBCAA). In real tap water from San Jose, CA, total HAAs measured 35.62 ppb, with HAA5 at 30.21 ppb—well below the EPA MCL. Matrix diversion effectively prevented coelution of major inorganic ions and minimized source fouling, and MS source temperatures (200 °C) were optimized to maximize sensitivity, particularly for TCAA.

Benefits and Practical Applications

• Elimination of time-consuming extraction and derivatization steps reduces sample preparation by several hours.
• Reagent-free eluent generation eliminates manual preparation of hydroxide solutions.
• Automated matrix diversion improves MS stability and reduces maintenance.
• Simultaneous quantitation of multiple regulated and non-regulated species in one analysis enhances laboratory efficiency.

Future Trends and Potential Applications

Advances in IC-MS/MS automation and miniaturization could enable even higher throughput and field-deployable systems for on-site water monitoring. Expansion of target analyte lists to include emerging disinfection by-products (e.g., nitrosamines, per- and polyfluoroalkyl substances) and integration with online sampling platforms will support proactive water quality management. Machine-learning algorithms may further enhance peak integration and anomaly detection in routine monitoring.

Conclusion

EPA Method 557 using direct IC-MS/MS offers a robust, sensitive and streamlined approach for monitoring haloacetic acids, bromate and dalapon in drinking water. The combination of reagent-free chromatography, MS/MS selectivity and automated matrix handling delivers reliable quantitation at sub-ppb levels, meeting regulatory requirements while greatly simplifying laboratory workflows.

References

1. U.S. Environmental Protection Agency. Microbial Health Effects Tables: Potential Adverse Health Effects from High/Long-term Exposure to Hazardous Chemicals in Drinking Water. 2002.
2. EPA Method 552.1: Determination of Haloacetic Acids and Dalapon in Drinking Water by Ion Exchange Liquid-Solid Extraction and GC-ECD. Rev. 1.0, 1992.
3. EPA Method 552.2: Determination of Haloacetic Acids and Dalapon by Liquid-Liquid Extraction, Derivatization, and GC-ECD. Rev. 1.0, 1995.
4. EPA Method 552.3: Determination of Haloacetic Acids and Dalapon by Liquid-Liquid Microextraction, Derivatization, and GC-ECD. Rev. 1.0, 2003.
5. EPA Method 557: Determination of Haloacetic Acids, Bromate, and Dalapon in Drinking Water by IC-ESI-MS/MS. Rev. 1.0, 2009.
6. Slingsby R.; Saini C.; Pohl C.; Jack R. Measurement of Haloacetic Acids in Drinking Water Using IC-MS/MS–Method Performance. Pittcon, New Orleans, LA, 2008.