Fast and rugged method for low-cost determination of anions in water

Significance of the Topic

Ion chromatography (IC) is a cornerstone technique for the routine monitoring of inorganic anions in various water matrices, including surface, ground, drinking, and wastewater. Regulatory frameworks such as the U.S. EPA’s Safe Drinking Water Act and Clean Water Act mandate precise and reliable anion analysis to ensure public health and environmental protection. A fast, cost-effective, and robust IC method enhances laboratory throughput and compliance monitoring capabilities.

Objectives and Study Overview

This application brief demonstrates a streamlined method for the determination of common inorganic anions in drinking water using a low-cost Thermo Scientific™ Dionex™ Easion™ IC system operated in Displacement Chemical Regeneration (DCR) mode. The study employs the high-efficiency Dionex IonPac™ AS29-Fast-4 µm column to achieve rapid separation within 10 minutes, meeting performance requirements of U.S. EPA Method 300.1.

Methodology and Instrumentation

• Eluent: Isocratic 4.5 mM sodium carbonate / 2.0 mM sodium bicarbonate.
• Regenerant: 50 mM sulfuric acid in DCR mode.
• Flow rate: 1.0 mL/min, injection volume: 25 µL (full loop), ambient column temperature.
• Autosampler filtration: 5 mL PolyVials with 20 µm filter caps enable in-vial sample cleanup.
• Calibration: Seven-level mixed standards covering typical regulatory ranges for fluoride, chloride, nitrite-N, bromide, nitrate-N, phosphate-P, and sulfate.

Instrumentation

• Dionex Easion IC system with high-pressure non-metallic pump.
• Dionex IonPac AG29-Fast-4 µm guard column (4 × 30 mm) and AS29-Fast-4 µm analytical column (4 × 150 mm).
• Dionex AS-DV Autosampler equipped with PolyVials and filter caps.
• Dionex ACRS 500 chemically regenerated suppressor (4 mm) operating in DCR mode.
• Conductivity detector and Thermo Scientific™ Chromeleon™ 7.2.10 data system.

Main Results and Discussion

• Separation of seven anions achieved in under 10 minutes with baseline resolution.
• Linearity for all analytes displayed coefficients of determination (r²) between 0.995 and 1.000 over relevant concentration ranges.
• Analysis of a municipal drinking water sample revealed chloride (3.84 mg/L) and sulfate (1.96 mg/L) as major anions; fluoride, nitrite, and nitrate levels were below their respective Maximum Contaminant Levels (MCLs).
• The integrated autosampler filter caps minimized sample preparation steps, demonstrating method ruggedness and suitability for high-ionic-strength or variable pH samples without pretreatment.

Benefits and Practical Applications

• Low-cost, single-channel IC setup tailored for routine compliance monitoring.
• Rapid analysis increases laboratory throughput for water quality testing.
• Automated inline filtration reduces manual sample handling and potential contamination.
• Robust performance across diverse water types supports regulatory testing laboratories, environmental monitoring, and quality control in industrial processes.

Future Trends and Opportunities

• Expansion of the method to include additional inorganic and organic anions for comprehensive water profiling.
• Integration of IC systems with laboratory information management systems (LIMS) for end-to-end automation.
• Development of miniaturized or field-portable IC platforms for on-site water monitoring.
• Advancements in suppressor technology and column chemistries to further shorten analysis times and enhance sensitivity.

Conclusion

The presented DCR-based IC method employing the Dionex Easion IC system and IonPac AS29-Fast-4 µm column offers a fast, rugged, and cost-effective solution for the determination of inorganic anions in drinking water. High resolution, strong linearity, and automated filtration make the approach ideal for routine regulatory compliance and quality assurance in water analysis.

References

1. U.S. Environmental Protection Agency. National Primary Drinking Water Regulations. Accessed May 27, 2020.
2. U.S. EPA Method 300.1: The Determination of Inorganic Anions in Water by Ion Chromatography; Rev 1.0; USEPA Office of Water, Cincinnati, OH, 1997.
3. Thermo Scientific™ Dionex™ Inorganic Anion Analysis by EPA 300.0 & 300.1. Accessed May 27, 2020.
4. Thermo Scientific Application Note 73607: Determination of Inorganic Anions in Drinking Water, Wastewater, and High Ionic Strength Water; Sunnyvale, CA, 2020.