Determination of inorganic anions in drinking water using a compact ion chromatography system

Importance of the Topic

The reliable quantification of common inorganic anions in drinking water is critical for ensuring public health and regulatory compliance. Ion chromatography (IC) methods, such as EPA Methods 300.0/300.1, are widely accepted for this purpose due to their sensitivity, selectivity, and ability to analyze multiple anions in a single run.

Objectives and Study Overview

This study demonstrates the application of a compact Thermo Scientific™ Dionex™ Aquion™ ion chromatography system for the determination of seven anions (fluoride, chloride, nitrite, bromide, nitrate, phosphate, and sulfate) in drinking water, following U.S. EPA Method 300.1. Key goals included:

• Establishing a simple, cost-effective IC setup
• Validating calibration, detection limits, and quantitation limits
• Evaluating method precision, accuracy, and recovery in tap and bottled water samples

Methodology

An isocratic separation was performed using a 4 × 250 mm Thermo Scientific™ Dionex™ IonPac™ AS22 analytical column with a 4 × 50 mm AG22 guard column. The eluent consisted of 4.5 mM Na₂CO₃ and 1.4 mM NaHCO₃ prepared by diluting a commercial concentrate. Suppressed conductivity detection was achieved with a Dionex AERS™ 500 Carbonate Electrolytically Regenerated Suppressor in recycle mode at 31 mA.

Chromatographic conditions:

• Flow rate: 1.2 mL/min
• Column temperature: 30 °C
• Injection volume: 10 µL
• Run time: 15 min

Used Instrumentation

• Dionex Aquion IC system with AS-DV autosampler (5 mL vials)
• IonPac AS22 analytical column and AG22 guard column
• Dionex AERS 500 Carbonate suppressor
• Chromeleon™ Chromatography Data System (CDS)

Main Results and Discussion

Calibration over 0.2–20 mg/L yielded linearity coefficients (r²) above 0.9999 for all anions. Estimated limits of detection ranged from 0.013 mg/L (fluoride) to 0.092 mg/L (phosphate), with corresponding quantitation limits (0.044 mg/L to 0.191 mg/L). Baseline noise was low (2.8–3 nS/min).

Analysis of tap and bottled water showed:

• Tap water: fluoride 0.73 mg/L, chloride 6.08 mg/L, nitrite 0.20 mg/L, nitrate 0.32 mg/L, phosphate 0.27 mg/L, sulfate 3.48 mg/L
• Bottled water: chloride 4.39 mg/L, nitrate 0.08 mg/L, sulfate 13.4 mg/L

Method accuracy was evaluated by spiking samples at 2.5 and 5.0 mg/L levels. Recoveries ranged from 95% to 104%, and precision (RSD) was typically below 1%.

Benefits and Practical Applications

• Compact, user-friendly system ideal for routine water quality monitoring
• Minimal eluent preparation reduces errors and downtime
• High sensitivity and reproducibility comply with EPA requirements
• Suitability for municipal, industrial, and bottled water testing labs

Future Trends and Applications

Advances in IC technology and miniaturization may further reduce instrument footprint and reagent consumption. Integration with automated sampling, advanced data analytics, and remote operation can enhance throughput and compliance tracking. Emerging applications include coupling IC with mass spectrometry for trace-level speciation and the analysis of anions in more complex matrices.

Conclusion

The Thermo Scientific Dionex Aquion IC system provides a robust, efficient platform for quantifying key inorganic anions in drinking water per EPA Method 300.1. The method offers excellent linearity, low detection limits, and strong accuracy and precision, making it a practical choice for laboratories focused on water quality assurance.

References

1. U.S. Environmental Protection Agency. Method 300.1: Determination of Inorganic Anions in Drinking Water by Ion Chromatography, Revision 1, 1997.
2. Thermo Scientific Dionex Aquion Ion Chromatography System Operator’s Manual, P/N 22176-97003, 2016.
3. Thermo Scientific Dionex AERS 500 Suppressor Product Manual, P/N 031956, 2018.
4. Thermo Scientific Dionex AS-DV Autosampler Operator’s Manual, P/N 065259, 2012.
5. Thermo Scientific Dionex IonPac AS22 Column Product Manual, P/N 065119-08, 2013.