Determination of inorganic anions in drinking water, wastewater, and high ionic strength water

Importance of the topic

Accurate monitoring of inorganic anions in water is critical for public health and environmental protection. Regulations such as the Safe Drinking Water Act and the Clean Water Act require reliable analysis of anions including fluoride, chloride, nitrite, bromide, nitrate, phosphate, and sulfate. High ionic strength samples and extreme pH values pose challenges for routine ion chromatography applications.

Aims and overview of the study

This application note evaluates the performance of a Thermo Scientific Dionex IonPac AS29-Fast-4µm anion exchange column on an RFIC system. The goal is to demonstrate rapid separation and quantitation of common inorganic anions in drinking water, wastewater, and samples with high ionic strength, and to compare results with a conventional AS4A-SC column specified in U.S. EPA Method 300.1.

Methodology and instrumentation

Analysis was performed on a Dionex ICS-5000+ RFIC system with suppressed conductivity detection and eluent generation. Key parameters included isocratic elution with 4.5 mM carbonate and 2.0 mM bicarbonate at 1.0 mL/min, 10 µL injections, and column temperature of 30 °C. Sample preparation was limited to 0.2 µm filtration and dilution for high chloride samples when required.

Used instrumentation

• Dionex ICS-5000+ SP/DP Pump module
• Dionex ICS-5000+ EG Eluent Generator with high-pressure degasser
• Dionex ICS-5000+ DC Conductivity Detector with ADRS 600 suppressor
• Dionex AS-AP Autosampler with 10 µL loop
• Dionex IonPac AG29-Fast-4µm guard column (4 × 30 mm)
• Dionex IonPac AS29-Fast-4µm analytical column (4 × 150 mm)

Main results and discussion

The AS29-Fast-4µm column achieved baseline separation of seven anions plus carbonate in under 10 minutes with excellent resolution of early eluting species. Compared with the AS4A-SC column, the AS29-Fast-4µm column tolerated high sample ionic strength and pH extremes without pretreatment. Eluent consumption was reduced by 50%. Calibration was linear across 0.01–500 mg/L (up to 1000 mg/L for chloride) with coefficients of determination >0.995. Method detection limits ranged from 0.003 to 0.035 mg/L. Retention time and peak area precisions were better than 0.1% and 0.7% RSD respectively.

Benefits and practical applications

Rapid run time and minimal sample preparation streamline routine compliance testing. High capacity and selectivity enable direct analysis of drinking water, wastewater, and industrial process streams with high salt content. Low eluent consumption and robust performance reduce operating costs and downtime.

Future trends and potential applications

Integration of inline sample cleanup cartridges for complex matrices may further simplify workflows. Coupling high-capacity anion columns with mass spectrometry can expand detection of emerging anionic contaminants. Advances in suppressor technology and column materials will continue to improve sensitivity and durability for real-time monitoring.

Conclusion

The Dionex IonPac AS29-Fast-4µm column on an RFIC system provides a fast sensitive and robust solution for determination of inorganic anions across a wide concentration range and challenging sample matrices. It offers clear advantages over traditional columns for regulatory compliance and industrial monitoring.

Reference

1. U.S. EPA National Primary Drinking Water Regulations 40 CFR Part 141 (1998)
2. U.S. EPA Clean Water Act National Pollutant Discharge Elimination System
3. U.S. EPA Method 300.0 Rev 2.1 Ion Chromatography for Water (1993)
4. U.S. EPA Method 300.1 Ion Chromatography for Water (1997)
5. U.S. EPA NPDES Permits Program
6. Greenberg AE Clesceri LS Eaton AD Standard Methods for Examination of Water and Wastewater 18th ed. (1992)
7. ASTM D4327-97 Standard Test Methods for Anions in Water by Ion Chromatography (1999)
8. Thermo Scientific Drinking Water Analysis Guide (2017)
9. Thermo Scientific Application Note 135 Inorganic Anions in Wastewater (2012)
10. Thermo Scientific Application Note 154 Inorganic Anions in Environmental Waters (2003)
11. Thermo Scientific Application Update 197 Anion Determinations in Wastewater (2016)
12. Thermo Scientific Application Update 196 Anion Determinations in Drinking Water (2016)
13. Thermo Scientific Dionex Eluent Generator Cartridges Manual
14. Thermo Scientific Dionex Suppressor Product Manual
15. Thermo Scientific IonPac AS29-Fast-4µm Column Specifications