Low-cost determination of inorganic cations and ammonium in environmental waters

Importance of the Topic

Ion chromatography is a well-established technique for monitoring inorganic ions in environmental waters to meet regulatory requirements under the Safe Drinking Water Act and the Clean Water Act. Routine measurement of alkali and alkaline earth cations, as well as ammonium, supports drinking water safety, wastewater management, and aquatic ecosystem protection. A low-cost, integrated analysis platform can improve laboratory efficiency and reduce operational expenses.

Objectives and Study Overview

This work demonstrates a simplified, cost-effective method for the determination of six common cations (Li+, Na+, NH4+, Mg2+, K+, Ca2+) in municipal drinking water and wastewater samples. The study evaluates chromatographic performance, calibration linearity, and compliance with U.S. EPA aquatic life criteria for ammonia.

Methodology and Instrumentation

Standards were prepared in degassed deionized water (18 MΩ·cm) at concentrations ranging from sub-milligram to several hundred milligrams per liter. Mixed calibration solutions spanned 0.01–500 mg/L depending on the analyte. Samples included an unfiltered municipal tap water and a laboratory-supplied wastewater. The chromatographic method used isocratic elution with 35 mM methanesulfonic acid, chemical regeneration with 100 mM tetrabutylammonium hydroxide, and suppressed conductivity detection in DCR mode.

Used Instrumentation

• Dionex Easion IC system for isocratic, single-channel operation
• Dionex IonPac CS16 analytical column (3 × 250 mm) with CG16 guard column (3 × 50 mm)
• Dionex CCRS 500 chemically regenerated suppressor (2 mm) in DCR mode
• Dionex AS-DV autosampler with 5 mL filter-cap vials

Main Results and Discussion

All six cations were baseline-resolved within a 25-minute run. Calibration curves for Li+, Na+, Mg2+, K+, and Ca2+ were linear with r² ≥ 0.999 over their respective ranges. Ammonium required a quadratic fit (r² = 0.997) over 0.05–125 mg/L. Analysis of real samples showed low concentrations in municipal water (e.g., Na ~20 mg/L, Ca ~11 mg/L, NH4+ <1 mg/L) and elevated levels in wastewater (e.g., Na ~146 mg/L, Mg ~28 mg/L), with both samples meeting U.S. EPA Criterion Continuous Concentration (<1.9 mg TAN/L) and Criterion Maximum Concentration (<17 mg TAN/L) for ammonia.

Benefits and Practical Applications

The integrated Easion IC system offers a user-friendly, low-cost solution for routine environmental monitoring laboratories. Advantages include minimal hardware complexity, reduced maintenance through chemical regeneration, and compatibility with standard compliance protocols.

Future Trends and Applications

Emerging developments may extend this platform to trace anion and metal analysis, incorporate automated sample preparation, enable field-deployable configurations, and integrate advanced suppression chemistries for even greater sensitivity. Software-driven quality control and cloud-based data management will further enhance environmental compliance monitoring.

Conclusion

A cost-effective Dionex Easion IC method with DCR suppression has been validated for accurate determination of six inorganic cations and ammonium in environmental water samples. The approach meets regulatory criteria and delivers robust performance for routine laboratory and field applications.

References

1. U.S. EPA. National Primary Drinking Water Regulations. 2020.
2. U.S. EPA Method 300.1: Determination of Inorganic Anions by Ion Chromatography. Rev. 1.0, 1997.
3. U.S. EPA. Aquatic Life Criteria – Ammonia. 2013.
4. Thermo Fisher Scientific Application Note 141: Determination of Inorganic Cations and Ammonium by Ion Chromatography. 2001.