Low-cost determination of anions in municipal drinking water

Significance of the Topic

The accurate determination of inorganic anions in municipal drinking water is essential for regulatory compliance and public health protection. Ion chromatography (IC) is a well‐established analytical technique endorsed by the U.S. EPA for monitoring contaminants such as fluoride, nitrite, and nitrate under the Safe Drinking Water Act and Clean Water Act.

Objectives and Study Overview

This study demonstrates a low-cost, isocratic IC method for routine quantification of common inorganic anions in drinking water. The work employs the Thermo Scientific™ Dionex™ Easion™ Ion Chromatography system operated in Displacement Chemical Regeneration (DCR) mode, coupled with the Dionex™ AS-DV autosampler, to meet U.S. EPA Method 300.1 requirements.

Methodology and Instrumentation

Sample preparation and calibration were performed using degassed ultrapure water. Individual 1000 mg/L anion stock solutions were diluted to prepare mixed calibration standards covering typical regulatory ranges. A local municipal drinking water sample was analyzed without additional filtration.

• IC System: Thermo Scientific Dionex Easion IC in DCR mode
• Auto-sampler: Thermo Scientific Dionex AS-DV
• Columns: Dionex IonPac AG22 (4 × 50 mm) guard and AS22 (4 × 250 mm) analytical
• Eluent: 4.5 mM Na₂CO₃ / 1.4 mM NaHCO₃
• Suppressor: ACRS 500 (4 mm), chemical regeneration with 50 mM H₂SO₄
• Detection: Suppressed conductivity
• Data system: Thermo Scientific Chromeleon 7.2.10

Main Results and Discussion

Baseline separation of seven anions (fluoride, chloride, nitrite, bromide, nitrate, phosphate, sulfate) was achieved within 15 minutes. Calibration curves exhibited strong linearity (r² = 0.997–1.000) over concentration ranges relevant to regulatory limits. Analysis of a municipal water sample yielded:

• Chloride: 3.41 mg/L
• Sulfate: 1.65 mg/L
• Fluoride: 0.57 mg/L (below MCL of 4 mg/L)
• Nitrite-N: 0.04 mg/L (below MCL of 1 mg/L)
• Nitrate-N: 0.05 mg/L (below MCL of 10 mg/L)
• Bromide and phosphate at trace levels

All measured values complied with U.S. EPA drinking water standards.

Benefits and Practical Applications

The integrated Easion IC system coupled with the AS-DV autosampler offers a cost‐effective, compact solution for routine water quality laboratories. Key advantages include minimal reagent consumption, rapid isocratic operation, and reliable suppressed conductivity detection suited for high‐throughput compliance monitoring.

Future Trends and Potential Applications

Advancements in miniaturized IC systems, automated sample handling, and cloud‐based data processing will further streamline anion analysis. Emerging applications may include on‐site portable monitoring, expanded analyte panels (e.g., organic acids), and integration with remote water quality networks for real‐time surveillance.

Conclusion

This work validates a simple, robust, low‐cost ion chromatography method for accurate quantification of inorganic anions in drinking water. The Dionex Easion IC system in DCR mode meets regulatory requirements and supports efficient routine monitoring in municipal water laboratories.

References

1. U.S. EPA National Primary Drinking Water Regulations. 2020.
2. U.S. EPA Method 300.1: Determination of Inorganic Anions in Water by Ion Chromatography; Rev 1.0; 1997.
3. Thermo Fisher Scientific. Inorganic Anions Analysis by EPA 300.0 & 300.1; 2020.