Low-cost determination of anions in municipal drinking water

Significance of the topic

The monitoring of inorganic anions in drinking water is critical for public health and regulatory compliance. Anions such as fluoride, nitrite and nitrate have maximum contaminant levels defined by the U.S. EPA under the Safe Drinking Water Act and Clean Water Act. Fast, reliable and cost-effective analytical methods are required to ensure safe water supplies and streamline routine laboratory operations.

Objectives and study overview

This study demonstrates a rapid ion chromatography (IC) method for the determination of seven common inorganic anions in municipal drinking water. The goal is to validate a turnkey, low-cost system based on the Thermo Scientific™ Dionex™ Easion™ IC platform paired with a Dionex IonPac™ AS22-Fast-4 µm column and AS-DV autosampler for compliance monitoring per U.S. EPA Method 300.1.

Methodology and Instrumentation used

The analysis was performed in isocratic mode with suppressed conductivity detection using displacement chemical regeneration (DCR). Key components and consumables included:

• Dionex Easion IC system (single-channel, low-cost pump)
• Dionex AS-DV autosampler with 5 mL filtered PolyVial™ vials
• Dionex ACRS 500 chemically regenerated suppressor (4 mm)
• Dionex IonPac AG22-Fast-4 µm guard column (4 × 30 mm) and AS22-Fast-4 µm analytical column (4 × 150 mm)
• DCR reagents and AS22 eluent concentrate (100×)
• Chromeleon™ 7.2.10 chromatography workstation

Calibration standards (0.1–100 mg/L) were prepared from 1000 mg/L stock solutions in 18 MΩ·cm DI water. The eluent comprised 4.5 mM Na2CO3/1.4 mM NaHCO3 at 1.2 mL/min, with a 50 mM H2SO4 regenerant, 25 µL full-loop injection, ambient column temperature, and suppressed conductivity detection.

Results and Discussion

The AS22-Fast-4 µm column achieved baseline resolution of fluoride, chloride, nitrite, bromide, nitrate, phosphate and sulfate within 10 minutes, compared to 15 minutes for conventional AS22 columns. Calibration curves were linear (r² = 0.995–1.000). Analysis of a municipal drinking water sample showed chloride at 3.44 mg/L, sulfate at 1.96 mg/L, and fluoride (0.54 mg/L), nitrite (0.01 mg/L) and nitrate (0.06 mg/L) well below EPA MCLs.

Benefits and practical applications

The combined Easion IC/AS-DV system provides a simple, cost-efficient solution for routine anion monitoring. Reduced analysis time increases sample throughput by two injections per hour versus traditional methods. The integrated hardware and software streamline setup, data acquisition and compliance reporting in environmental, municipal and industrial laboratories.

Future trends and potential uses

Advances may include expanded analyte panels (e.g., organic acids), higher-throughput autosamplers, miniaturized or modular IC systems for field use, and automated data integration with laboratory information management systems. Method adaptation for emerging contaminants and real-time online monitoring represent further opportunities.

Conclusion

The Thermo Scientific™ Dionex™ Easion™ IC system with AS22-Fast-4 µm columns and AS-DV autosampler offers a rapid, reliable and affordable approach for compliance monitoring of inorganic anions in drinking water, meeting U.S. EPA requirements with enhanced laboratory efficiency.

References

1. National Primary Drinking Water Regulations. U.S. EPA (Accessed May 27, 2020).
2. EPA Method 300.1: Determination of Inorganic Anions in Water by Ion Chromatography, rev 1.0; U.S. EPA Office of Water; 1997.
3. Inorganic Anions Analysis by EPA 300.0 & 300.1. Thermo Fisher Scientific (Accessed May 27, 2020).
4. Dionex IonPac AS22-Fast-4 µm IC columns. Thermo Fisher Scientific (Accessed June 10, 2020).