Determination of Inorganic Cations and Ammonium in Environmental Waters by Ion Chromatography Using the Dionex IonPac CS16 Column

Significance of the Topic

Monitoring alkali and alkaline earth cations and ammonium in environmental waters is vital for ensuring drinking water safety, controlling corrosion through water hardness assessment, and complying with wastewater regulations. The traditional need for separate analytical procedures for inorganic cations and ammonium increases sample workload and may compromise data consistency. Ion chromatography enables simultaneous determination of multiple cations and ammonium in a single run, enhancing throughput and data quality.

Objectives and Study Overview

This study demonstrates a robust ion chromatography method using the Thermo Scientific Dionex IonPac CS16 column and electrolytically generated methanesulfonic acid (MSA) eluent. Key aims include evaluating linear dynamic range, method detection limits (MDLs), retention time precision, and analyte recovery in various environmental matrices. The influence of matrix interferences and column capacity on high ionic strength samples was assessed.

Methodology and Instrumentation

Samples were filtered and, for soil extracts, sonicated with either deionized water or MSA solution before injection. Eluent was generated in-line at 26 mM MSA using the Dionex EG40 eluent generator. Suppressed conductivity detection was performed with the CSRS ULTRA self-regenerating suppressor in autosuppression recycle mode.

Used Instrumentation

• Dionex DX-600 chromatography system or equivalent ICS series
• GP50 gradient pump with vacuum degas option
• EG40 eluent generator with EGC-MSA cartridge
• ED50A electrochemical detector with CSRS ULTRA suppressor
• AS50 autosampler with thermal compartment
• Thermo Scientific Dionex PeakNet chromatography software

Main Results and Discussion

Temperature control at 30 °C provided retention time reproducibility of ≤0.2% RSD; ambient operation was acceptable but less precise. Calibration was linear over three orders of magnitude for most cations (Li+, Na+, K+, Mg2+, Ca2+), while ammonium required a quadratic fit up to 40 mg/L. MDLs ranged from 0.19 to 2.64 μg/L, with precision and accuracy for seven injections typically below 1% RSD for retention time and peak area. Spike recoveries in reagent water, drinking water, wastewater, and soil extracts were within 80–120%, demonstrating robustness across matrices. The high capacity column resolved trace ammonium in the presence of a 10 000-fold higher sodium concentration. Acidic soil extracts (up to 100 mM H+) could be analyzed without pH adjustment, although periodic cleaning with acetonitrile may be required to maintain column performance.

Benefits and Practical Applications

This method consolidates multi-cation and ammonium analysis into a single, automated run, reducing sample preparation steps and operational costs. The high capacity IonPac CS16 column extends linear range and enhances resolution in high ionic strength samples, suitable for drinking water quality control, wastewater discharge monitoring, and soil extract analysis. The use of an eluent generator improves reproducibility and eliminates manual eluent preparation.

Future Trends and Opportunities

Integration with mass spectrometric detection could further enhance selectivity and lower detection limits for emerging contaminants. Miniaturization and portable IC systems may enable on-site environmental monitoring. Method adaptation for additional analytes, such as low-level transition metals or organic ions, could broaden application scope. Automated data processing and cloud-based reporting will streamline laboratory workflows and regulatory compliance.

Conclusion

The described ion chromatography method using the Dionex IonPac CS16 column and MSA eluent offers a high-capacity, precise, and versatile approach for simultaneous determination of common cations and ammonium in diverse environmental waters, meeting regulatory and quality control requirements.

References

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6. The Determination of Inorganic Anions in Water by Ion Chromatography; U.S. EPA Method 300.0; Cincinnati, Ohio, 1993.