Determination of Inorganic Anions in Drinking Water by Ion Chromatography

Significance of the Topic

Monitoring inorganic anions in drinking water is critical for public health and regulatory compliance. Fluoride, nitrite and nitrate levels are controlled to prevent fluorosis and methemoglobinemia. Other anions such as chloride and sulfate affect taste and aesthetics and are governed by secondary guidelines.

Objectives and Study Overview

The goal of this study was to evaluate ion chromatography methods for determination of common inorganic anions in drinking and environmental waters under conditions of US EPA Method 300.0. Two columns were compared: a latex-based agglomerated polymer column and a grafted methacrylate resin column. Method performance was assessed in terms of linearity, detection limits, precision and recovery in various water matrices.

Methodology and Instrumentation

Instrumentation

• Dedicated and modular ion chromatography systems with gradient pump, conductivity detector, automated sampler and chromatography workstation
• Self regenerating anion suppressor operated in recycle mode

Eluent preparation

• Low-strength carbonate bicarbonate eluents diluted from concentrates and helium pressured

Columns and conditions

• Column A: Ion exchange latex agglomerated material, 4 by 250 mm, 1.8 mM carbonate 1.7 mM bicarbonate, 2.0 mL per minute, run time under 8 minutes
• Column B: Grafted methacrylate resin, 4 by 250 mm, 3.5 mM carbonate 1.0 mM bicarbonate, 1.2 mL per minute, run time under 14 minutes

Sample preparation

• Reagent water fortified to prepare working standards and quality control samples
• Direct vial filtration for drinking and surface water, C18 cleanup for domestic wastewater, ultrasonic extraction for soil

Main Results and Discussion

Both columns delivered excellent linearity (r2 above 0.996) over 0.1 to 200 mg per liter. Method detection limits ranged from 2 to 20 micrograms per liter. Retention time precision was below 1 percent and peak area precision below 1 percent. Recoveries in drinking water, raw water, surface water, industrial and domestic wastewater and soil extracts were generally within 80 to 120 percent. The grafted resin column provided superior resolution of fluoride from void peaks and organic interferences, while the latex column offered faster analysis for low-ionic-strength matrices.

Benefits and Practical Applications

• Single chromatographic run replaces multiple colorimetric, titrimetric or electrode tests
• High sensitivity and specificity for regulatory compliance monitoring
• Automated sample introduction and analysis reduce labor and increase throughput
• Flexible configuration allows adaptation to drinking water, environmental and wastewater matrices

Future Trends and Potential Uses

Emerging trends include coupling ion chromatography with mass spectrometry for enhanced selectivity, development of higher capacity polymer materials to handle complex samples, integration of microfluidic IC for on-site monitoring and further advances in suppressor design to reduce maintenance.

Conclusion

Both evaluated columns meet US EPA requirements for inorganic anion analysis. The latex agglomerated column is recommended for rapid analysis of low-ionic-strength samples. The grafted methacrylate column offers improved resolution for fluoride and robustness in more challenging high-ionic-strength or organic-rich matrices.

References

1. US EPA Method 300.0 The Determination of Inorganic Anions in Water by Ion Chromatography 1993
2. Standard Methods for the Examination of Water and Wastewater 18th edition 1992 American Public Health Association
3. ASTM Standard Test Method for Anions in Water by Chemically Suppressed Ion Chromatography D4327-97