Determination of Sub-μg/L Bromate in Municipal and Natural Mineral Waters Using Preconcentration with Two-Dimensional Ion Chromatography and Suppressed Conductivity Detection

Significance of the Topic

The use of ozone as a disinfectant in municipal and bottled waters effectively inactivates chlorine-resistant pathogens and eliminates taste or residual by-products. However, ozonation of bromide-containing waters can generate trace levels of bromate, a probable human carcinogen. Regulatory bodies in the U.S. and Europe have established maximum contaminant levels (MCLs) for bromate as low as 3–10 µg/L, driving the need for sensitive, accurate analytical methods.

Objectives and Study Overview

This work evaluates a two-dimensional ion chromatography (2-D IC) method with preconcentration and suppressed conductivity detection for quantifying bromate at sub-µg/L levels in high-ionic-strength matrices. Key goals included:

• Lowering the detection limit compared to existing EPA methods.
• Avoiding extensive sample pretreatment or dilution.
• Demonstrating robust performance in municipal and natural mineral waters.

Instrumentation

A Thermo Scientific Dionex ICS-3000 Reagent-Free IC system was configured in two dimensions:

• First dimension: Dionex IonPac AG19 guard (4 × 50 mm) and AS19 analytical (4 × 250 mm) columns, KOH eluent generated by EGC II cartridge, ASRS ULTRA II suppressor (4 mm).
• Second dimension: Dionex IonPac AG24 guard (2 × 50 mm) and AS24 analytical (2 × 250 mm) columns, TAC-ULP1 concentrator (5 × 23 mm), ASRS ULTRA II suppressor (2 mm).
• Autosampler: Dionex AS with 5 mL syringe, 1000 µL loop.

Methodology

Samples (1000 µL) are injected into the first dimension, where matrix ions are diverted to waste and a 2 mL bromate‐enriched plug is transferred to the second dimension. A stepped KOH gradient (10–65 mM) separates bromate from co-eluting anions. Suppressed conductivity detection enables quantification.

Calibration standards (0.15–15 µg/L) produced a quadratic fit (r2 = 0.9995). The single-laboratory lowest concentration minimum reporting level (LCMRL) was 0.15 µg/L, and the method detection limit (LOD) was 0.036 µg/L.

Main Results and Discussion

The 2-D IC method delivered recoveries of 98–106% for bromate fortifications at 0.5 and 5.0 µg/L in reagent water, laboratory synthetic sample matrix, and two municipal waters. High-ionic-strength mineral waters (up to 1445 mg/L sulfate) achieved 95–104% recovery without dilution or cartridge cleanup after a minor adjustment of the cut window.

Benefits and Practical Applications

• Exceptional sensitivity (LOD 0.036 µg/L) surpassing EPA postcolumn methods.
• Direct injection of challenging matrices, eliminating sample preparation and cost.
• Fully automated 2-D workflow enhances reproducibility across laboratories.

Future Trends and Potential Uses

Advances in reagent-free eluent generation and microflow suppressors may further reduce detection limits and solvent consumption. Integration with mass spectrometry could enable simultaneous multi-analyte monitoring of disinfection by-products. Applications extend to quality assurance in water utilities and rapid screening in bottled water production.

Conclusion

The 2-D IC approach with preconcentration and suppressed conductivity detection provides a powerful, cost-effective tool for quantifying sub-µg/L bromate in high-ionic-strength drinking waters. Its low detection limit, high accuracy, and minimal sample handling support compliance with stringent regulatory standards.

References

1. U.S. EPA Method 300.1, Determination of Inorganic Anions in Drinking Water by Ion Chromatography, 1997.
2. U.S. EPA Method 317.0, Determination of Inorganic Oxyhalide Disinfection By-Products in Drinking Water Using Postcolumn Reagent Addition, 2001.
3. U.S. EPA Method 326.0, Ion Chromatography with Suppressor-Acidified Postcolumn Reagent for Bromate Analysis, 2002.
4. U.S. EPA Statistical Approach for the Determination of the Single-Laboratory LCMRL, 2004.
5. Brian DeBorba and Jeff Rohrer, Thermo Scientific Application Note 167, 2004.