Fast determination of chlorite, bromate, chlorate, dichloroacetic acid, and trichloroacetic acid in drinking water

Significance of the topic

Disinfection by-products (DBPs) form when common drinking water disinfectants react with inorganic or organic constituents. Several DBPs are associated with carcinogenicity and reproductive toxicity, so rapid, reliable monitoring is essential to protect public health and to verify compliance with drinking water standards. This application note presents a fast ion chromatography (IC) method for five regulated DBPs—chlorite, bromate, chlorate, dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA)—that meets Chinese regulatory needs while reducing analysis time compared with earlier procedures.

Objectives and overview of the study

The primary objective was to develop and validate a rapid, robust IC method using suppressed conductivity detection to quantify five DBPs in drinking water in under 21 minutes. The method aims to deliver low detection limits, good linearity, acceptable accuracy and precision, and practical suitability for routine monitoring in municipal laboratories.

Methodology

The method uses anion-exchange IC with a KOH gradient eluent. Key procedural points:

• Sample pre-treatment: filtration through 0.22 μm syringe filters prior to analysis.
• Chromatography: Thermo Scientific Dionex IonPac AS19-4μm analytical column (4 × 150 mm) with an AG19 guard (4 × 30 mm).
• Eluent: KOH gradient (6 mM initial, ramp to 20 mM, brief 50 mM step, return to 6 mM); total run time 21 min.
• Flow rate: 1.2 mL/min; injection volume: 250 μL; column temperature: 25 °C.
• Detection: suppressed conductivity using a dynamically regenerated suppressor in recycle mode (ADRS 600); background conductance ~0.4 μS/min.
• System: Dionex Inuvion IC system with RFIC eluent generation and degasser; method operates at system backpressure near 2,800 psi.

Used instrumentation

Instrumentation and consumables explicitly reported in the study include:

• Dionex Inuvion IC system with RFIC (P/N 22185-60108)
• Dionex AS-AP autosampler
• Dionex IonPac AS19-4μm analytical column (4 × 150 mm) and IonPac AG19-4μm guard column (4 × 30 mm)
• Dionex ADRS 600 anion dynamically regenerated suppressor (4 mm)
• Dionex EGC 500 KOH eluent generator cartridge
• Dionex CR-ATC 600 continuously regenerated anion trap column
• Dionex RFIC eluent degasser
• Chromeleon CDS software (v7.3.2) and ultrapure water (18.2 MΩ·cm)

Main results and discussion

Separation performance and run time:

• All five analytes eluted within about 15 minutes; total method cycle time was 21 minutes—approximately a 50% reduction versus the referenced longer (≈40 min) method.
• Use of smaller stationary-phase particles (4 μm) and a shorter analytical column (150 mm) provided improved efficiency and resolution while maintaining acceptable backpressure for modern high-pressure IC systems.
• Minor chromatographic overlap between chlorite and bromate was observed but did not compromise quantification across the tested concentration ranges.

Analytical figures of merit:

• Linearity: correlation coefficients R ≥ 0.999 for all analytes across the reported calibration ranges.
• Detection limits (instrumental S/N=3) were in the sub- to low-μg/L range: chlorite 0.26 μg/L, bromate 0.34 μg/L, DCAA 0.44 μg/L, chlorate 0.46 μg/L, TCAA 1.23 μg/L. Corresponding LOQs (S/N=10) ranged roughly 0.9–4.1 μg/L.
• Accuracy and precision: spike recoveries in Shanghai drinking water ranged from about 90% to 107% with RSDs ≤ 2.0% (n=3), demonstrating good trueness and repeatability for routine monitoring.
• Real sample testing: a municipal drinking water sample contained chlorate at 181 μg/L; other target DBPs were below the method detection limits. The detected chlorate concentration remained well below the GB 5749-2022 limit of 700 μg/L.

Benefits and practical applications of the method

The validated IC method offers several practical advantages for water quality laboratories:

• Faster throughput: nearly halved run time improves sample throughput and reduces per-sample consumable use.
• Regulatory suitability: LODs and linear ranges meet or exceed requirements for regulated DBPs under GB 5749-2022.
• Cost-efficiency: conductivity detection with eluent generation avoids the higher cost and complexity of mass-spectrometric systems for the targeted analyte panel.
• Robustness: stable retention times (RSD < 0.3%) and peak area precision (RSD < 0.9%) support routine implementation.

Limitations and considerations

• High-level common ions in drinking water (chloride, nitrate, sulfate, carbonate) may complicate separations for broader analyte panels; careful method development and gradient optimization remain important.
• TCAA had higher LOD/LOQ than the other analytes; laboratories requiring lower pg–ng/L detection for certain DBPs may need IC-MS/MS approaches.
• The method operates at high pressure (~2,800 psi); older IC hardware not rated for such pressures may be unsuitable.

Future trends and applications

Anticipated developments and extensions in DBP analysis include:

• Broader panels and lower detection limits via coupling IC to tandem mass spectrometry (IC–MS/MS) to capture a wider range of HAAs and trace DBPs.
• Automation and on-line sample preconcentration (e.g., on-line SPE) to improve sensitivity and reduce manual sample handling.
• Miniaturized and higher-efficiency stationary phases (sub-2 μm and core–shell technologies) for even faster separations, balanced against system pressure limits.
• Integration with laboratory information management systems (LIMS) and routine compliance workflows to streamline reporting.
• Development of green analytical approaches using reduced solvent usage and optimized reagent consumption.

Conclusion

This application demonstrates a practical, high-throughput IC method for five regulated DBPs in drinking water using KOH gradient elution and suppressed conductivity detection. By employing a 4 μm IonPac AS19 column and a modern RFIC platform, the method achieves rapid separation (21 min total), sub- to low-μg/L detection capabilities, excellent linearity, and reliable accuracy and precision—making it suitable for routine monitoring and regulatory compliance testing in modern water testing laboratories.

Reference

1. Xinyuan Yi, Xinlu Qu, Xin Long, et al. Research progress on chemical properties, transformation, and toxicity of typical disinfection by-products in drinking water. Asian Journal of Ecotoxicology, 2023, 18(02):97–110.
2. Sandhya Rao Poleneni. Chapter 13 - Global disinfection by-products regulatory compliance framework overview, in Disinfection By-products in Drinking Water: Detection and Treatment, edited by Majeti Narasimha Vara Prasad. Butterworth-Heinemann, 2020.
3. Xin Zhang, Charanjit Saini, Chris Pohl, and Yan Li. Thermo Scientific Application Note AN73343: Fast Determination of Nine Haloacetic Acids, Bromate, and Dalapon at Trace Levels in Drinking Water Samples by Tandem IC-MS/MS. 2020.