Determination of Inorganic Anions in Municipal Water Using High-Pressure Modular Capillary Ion Chromatography

Importance of the Topic

Ion chromatography is a fundamental analytical technique for monitoring inorganic anions in environmental water samples. Regulatory frameworks such as the Clean Water Act and Safe Drinking Water Act in the US require precise quantification of anions to ensure public health and environmental safety. High throughput and reliable detection of species like fluoride, nitrate, and sulfate are critical for compliance and water quality management.

Goals and Study Overview

This study aims to demonstrate rapid separation of inorganic anions in municipal water using a high-pressure capillary ion chromatography (HPIC) system. By employing a 4 micrometer particle column and elevated flow rates, the work evaluates reductions in analysis time and improvements in sample throughput for both drinking and wastewater.

Methodology

Sample preparation involved dilution of municipal drinking water fivefold and wastewater samples 1000-fold, followed by filtration through a 0.2 micrometer syringe filter. A 23 mM KOH eluent was generated electrolytically and delivered at flow rates up to 0.025 mL per minute. Conductivity detection was performed in recycle mode using a capillary suppressor, with column temperature maintained at 30 °C and injection volumes of 0.4 µL.

Used Instrumentation

• Dionex ICS-5000+ HPIC Reagent-Free capillary system including dual pump, eluent generator, and detector modules with IC Cube and degas cartridge
• Dionex AS-AP autosampler with 10 mL vial carousel
• Dionex IonPac AS18-4 µm capillary separation column (0.4 × 150 mm) and AG18-4 µm guard column
• Electrolytic eluent generator cartridge (EGC-KOH), CR-ATC trap column, CRD bypass cartridge, ACES 300 suppressor
• High-pressure fittings, degas cartridges, and standard labware

Main Results and Discussion

Increasing the flow rate from 0.010 to 0.025 mL per minute reduced run times from about seven to under three minutes while preserving resolution for nine target anions. Operating at approximately 3800 psi was well within the system limit of 5000 psi. Daily eluent and waste consumption remained low at approximately 36 mL, minimizing operating costs.
In municipal drinking water samples, fluoride concentrations spanned 0.05 to 1.14 mg/L and nitrate levels ranged from 0.16 to 17 mg/L, reflecting substantial variability across water sources. Analysis of wastewater effluents showed chloride, nitrate, and sulfate levels varying by factors up to 25 across treatment stages, demonstrating the method’s dynamic range and sensitivity.

Benefits and Practical Applications

• Dramatic reduction in analysis time enables high sample throughput
• Low eluent and waste generation lower operating costs and environmental impact
• High-pressure capability and fine resin particles ensure sharp peaks and robust resolution
• Suitable for compliance monitoring under US EPA Methods 300.0 and 300.1

Future Trends and Potential Applications

Advances may include further miniaturization of IC systems, integration with mass spectrometry for enhanced selectivity, and development of automated inline sampling for real-time water quality monitoring. Continued optimization of column chemistries and suppressor technologies will support lower detection limits and expanded analyte coverage.

Conclusion

The combination of the Dionex ICS-5000+ HPIC capillary system and IonPac AS18-4 µm column provides a rapid, efficient, and cost-effective solution for the determination of inorganic anions in municipal water samples. High-pressure operation at increased flow rates achieves fast run times without sacrificing chromatographic performance.

References

• Greenberg AE, Clesceri LS, Eaton AD, Eds. Standard Methods for the Examination of Water and Wastewater, 18th ed.; American Public Health Association, Washington, DC, 1992.
• ASTM D4327-97, Standard Test Methods for Anions in Water by Chemically Suppressed Ion Chromatography; ASTM, West Conshohocken, PA, 1999.
• EPA, Fluoride: Dose-Response Analysis for Non-cancer Effects, EPA Report No. 820-R-10-019, Washington, DC, 2010.
• EPA, Monitored Natural Attenuation of Inorganic Contaminants in Ground Water, EPA Report No. 600-R-07-140, Cincinnati, OH, 2007.
• EPA Method 300.0 Rev 2.1, Determination of Inorganic Anions in Water by Ion Chromatography; US EPA, Cincinnati, OH, 1993.
• EPA Method 300.1 Rev 1.0, Determination of Inorganic Anions in Drinking Water by Ion Chromatography; US EPA, Cincinnati, OH, 1997.
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• Thermo Fisher Scientific. Application Note 154, Determination of Inorganic Anions in Environmental Waters Using a Hydroxide-Selective Column, Dionex LPN 1539, Sunnyvale, CA, 2003.