Improved Determination of Trace Perchlorate in Drinking Water Using 2D-IC

Significance of the Topic

Perchlorate is a persistent environmental contaminant affecting drinking, ground, and surface waters worldwide. It disrupts thyroid function by inhibiting iodine uptake and originates from both natural processes (atmospheric reactions, desert deposits) and anthropogenic sources (rocket propellants, fireworks, ordnance). Accurate quantification of trace perchlorate is essential for public health monitoring and regulatory compliance.

Objectives and Study Overview

This study aimed to develop an enhanced two-dimensional ion chromatography (2D-IC) method—building on EPA Method 314.2 and Thermo Fisher Application Note 178—to determine sub-ppb levels of perchlorate in drinking water. By replacing the original 4 mm/2 mm column configuration with a 2 mm/0.4 mm analytical-capillary hybrid system, the goal was to increase sensitivity, reduce reagent consumption, and maintain or improve method detection limits (MDLs) and reporting levels.

Methodology and Instrumentation

Reagents included high-purity sodium perchlorate standard and mixed anion solutions. A Thermo Scientific Dionex ICS-5000 Hybrid IC system with dual pumps, eluent generators (analytical and capillary KOH cartridges), suppressed conductivity detectors (ASRS 300 and ACES 300), and a DC chromatography compartment was used. Separations were performed in two dimensions:

• First dimension: 2 × 250 mm IonPac AS20 (with AG20 guard) at 0.25 mL/min using 35–60 mM KOH gradient;
• Second dimension: 0.4 × 250 mm capillary IonPac AS16 (with AG16 capillary guard) at 0.01 mL/min with 65 mM KOH;
• Sample focusing on a monolithic capillary concentrator (IonSwift MAC-200) between dimensions;
• Autosampling by Dionex AS-AP with 500 µL injection loops.

Main Results and Discussion

The hybrid 2 mm/0.4 mm configuration achieved an MDL of 0.005 µg/L (5 ng/L) and a linear range of 0.01–10 µg/L (R² = 0.9998). The laboratory computed a lowest concentration minimum reporting level (LCMRL) of 0.05 µg/L with 99% confidence. Recovery tests in reagent water, synthetic high-ionic-strength water (1000 mg/L each of Cl⁻, SO₄²⁻, HCO₃⁻), and three drinking water sources showed:

• 0.2 µg/L spike recoveries: 93–110% (RSD < 3%);
• 2.0 µg/L spike recoveries: 101–106% (RSD < 1%);

The narrower capillary second dimension provided a 25-fold sensitivity gain versus the first dimension, versus a four-fold gain in the previous 4 mm/2 mm setup. Matrix interferences were efficiently removed in the first dimension, and perchlorate peaks were well resolved in the second.

Benefits and Practical Applications

The improved 2D-IC method offers:

• Enhanced sensitivity and lower MDL for regulatory and research needs;
• Reduced eluent and reagent consumption through lower flow rates;
• Improved column lifetime by minimizing sample load and matrix fouling;
• Reagent-free KOH eluent generation and automated suppression for robust, low-maintenance operation;
• Applicability to high-ionic-strength and drinking water matrices without extensive sample pretreatment.

Future Trends and Potential Applications

Emerging trends include further miniaturization of capillary IC to boost sensitivity, integration with mass spectrometric detection for confirmatory analysis, and online coupling for real-time monitoring. Expanding this approach to other challenging anions at trace levels and adapting portable IC systems could broaden field applications.

Conclusion

This work demonstrates a significant advancement in perchlorate analysis by implementing a 2 mm/0.4 mm 2D-IC system. The method achieves sub-ppb detection, high accuracy and precision, and streamlined operation, making it ideal for routine monitoring of drinking water and environmental samples.

References

1. U.S. EPA Method 314.2: Determination of Perchlorate in Drinking Water by Two-Dimensional Ion Chromatography.
2. Thermo Fisher Scientific Application Note 178: Improved Trace Perchlorate Determination in Drinking Water via 2D-IC.
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