Efficient and Fast Separations of Inorganic Anions in Water Samples Using a 4 μm Particle Size Microbore Column with a High-Pressure Ion Chromatography System

Significance of the Topic

Inorganic anion analysis in environmental water is essential for monitoring water quality, ensuring regulatory compliance, and protecting public health. Rapid, high-resolution separation techniques increase laboratory throughput and minimize analysis time, which is critical for routine testing of drinking and wastewater.

Goals and Study Overview

This study aimed to demonstrate the performance advantages of a 4 µm resin particle size microbore ion-exchange column (Dionex IonPac AS18-4µm) operated on a high-pressure, reagent-free ion chromatography system (Dionex ICS-5000+ HPIC). Key objectives included comparing separation efficiency and run times against a 7.5 µm AS18-Fast column and evaluating sample analyses of municipal water.

Methodology and Instrumentation

An optimized reagent-free high-pressure ion chromatography setup was used:

• Dionex ICS-5000+ HPIC system with SP/DP Pump, EG Eluent Generator and high-pressure degas, DC Detector, and AS-AP Autosampler modules
• Inline eluent generation: 23 mM KOH produced by Thermo Scientific Dionex EGC 500 cartridge
• Anion trap column: Thermo Scientific Dionex CR-ATC 500
• Analytical column: Dionex IonPac AS18-4µm (2 × 150 mm), accompanied by AG18-4µm guard
• Suppressor: Thermo Scientific Dionex ASRS 300 self-regenerating anion suppressor (2 mm, recycle mode)
• Detector: Suppressed conductivity (15–22 mA), column temperature 30 °C, typical flow rates 0.25–0.38 mL/min

Results and Discussion

Comparative runs showed that the 4 µm microbore column halved sample loading and delivered sharper peaks with improved resolution relative to the 7.5 µm AS18-Fast column. By increasing flow rate to 0.38 mL/min, nine inorganic anions (fluoride, chlorite, chloride, nitrite, carbonate, bromide, sulfate, nitrate, chlorate) were fully separated in under 6 minutes at backpressures up to 3600 psi. Analysis of municipal drinking and wastewater samples resolved five key anions within 5 minutes, validating rapid environmental testing capability.

Benefits and Practical Applications

• Increased throughput: sub-6-minute anion separations accelerate routine water analysis
• High resolution: smaller particles yield sharper peaks and better discrimination
• Operational simplicity: reagent-free eluent generation reduces manual preparation and variability
• Wide applicability: suits drinking water and wastewater monitoring in municipalities and QA/QC labs

Future Trends and Applications

Anticipated advances include further reduction of particle size for sub-3-minute separations, integration with mass spectrometry for enhanced selectivity, automated inline sample preconcentration, and development of more compact, high-pressure systems. Sustainable approaches may focus on reducing water and energy consumption through smarter eluent recycling and microfluidic designs.

Conclusion

The combination of a 4 µm microbore IonPac AS18 column and a high-pressure reagent-free IC system significantly improves anion separation speed and resolution. This methodology supports high- throughput environmental water testing with robust reproducibility and streamlined operation.

References

1. U.S. EPA Method 300.0, Revision 2.1, Determination of Inorganic Anions in Water by Ion Chromatography, U.S. Environmental Protection Agency, 1993.
2. Thermo Fisher Scientific. Dionex IonPac AS18-4µm Hydroxide-Selective Anion-Exchange Capillary Column, Application Information, 2016.
3. Thermo Fisher Scientific. Dionex Technical Note 129: Configuring High-Pressure IC Systems for Analytical Flow Rates, 2012.
4. Thermo Fisher Scientific. ICS-5000+ Installation Instructions, Doc No. 065447, 2011.
5. Thermo Fisher Scientific. Application Note 154: Determination of Inorganic Anions in Environmental Water Using a Hydroxide-Selective Column, 2003.
6. Thermo Fisher Scientific. Application Brief 132: Determination of Anions in Municipal Drinking Water by Fast IC Using a Hydroxide Eluent, 2011.