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

Importance of the Topic

Water hardness and ammonium levels are key parameters in environmental monitoring, corrosion control, and regulatory compliance. Simultaneous detection of alkali and alkaline earth cations alongside ammonium streamlines analysis workflows and reduces sample handling.

Objectives and Overview of the Study

This work evaluates an ion chromatography method employing the IonPac CS16 high capacity cation exchange column with electrolytically generated methanesulfonic acid eluent and suppressed conductivity detection. The goal is to determine dissolved lithium, sodium, ammonium, potassium, magnesium, and calcium in drinking water, wastewater, and soil extracts in a single run while assessing linearity, detection limits, and interferences.

Methodology and Instrumentation Used

The method uses a Dionex DX-600 system with a GP50 pump, EG40 eluent generator with EGC-MSA cartridge, ED50A detector with DS3 stabilizer, CSRS-ULTRA suppressor, and AS50 autosampler. The separation employs a 5x50 mm CG16 guard column and a 5x250 mm CS16 analytical column at 30 C. Eluent is 26 mM MSA at 1.5 mL/min with a 10 µL injection. Suppressed conductivity detection in recycle mode at 100 mA ensures low background and noise. Samples are filtered through 0.45 µm IC syringe filters; soil extracts are prepared by ultrasonic extraction in water or eluent.

Main Results and Discussion

Retention time precision is under 0.2% RSD and peak area precision below 1% RSD. Calibration is linear over three orders of magnitude for most cations (r2>0.999), with a quadratic fit extending ammonium calibration to 40 mg/L. Method detection limits lie in the low microgram per liter range for all analytes. Spike recoveries in reagent water, wastewater, drinking water, and ASTM wastewater fall between 80 and 120%. The high capacity column resolves trace ammonium in the presence of a 10,000-fold excess of sodium and tolerates acidic matrices without pH adjustment.

Benefits and Practical Applications of the Method

The one-run IC method simplifies laboratory workflows by eliminating separate ammonia procedures and combining multi-cation analysis. Its high capacity and solvent compatibility make it suitable for diverse environmental samples and high ionic strength matrices, benefiting QA/QC, regulatory monitoring, and industrial analytics.

Future Trends and Possibilities for Application

Advances may include integration with mass spectrometry for species confirmation, further automation of eluent generation, miniaturized field-deployable IC systems, and expanded applications to complex industrial effluents and bioprocess monitoring.

Conclusion

The IonPac CS16 column combined with EG40-generated MSA and suppressed conductivity detection provides a robust, precise, and low-detection-limit method for simultaneous analysis of inorganic cations and ammonium in environmental waters and extracts, supporting efficient compliance and water quality assessment.

Instrumentation Used

• Dionex DX-600 system with GP50 pump and vacuum degas
• EG40 eluent generator equipped with EGC-MSA cartridge
• ED50A conductivity detector with DS3 stabilizer
• CSRS-ULTRA suppressor in recycle mode
• AS50 autosampler with thermal compartment
• IonPac CG16 guard column (5x50 mm) and IonPac CS16 column (5x250 mm)

References

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2. Standard Methods for the Analysis of Water and Wastewater, 18th Ed, American Public Health Assn, 1992, pp 4-75 to 4-85
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6. U S EPA Method 300.0, Determination of Inorganic Anions in Water by Ion Chromatography, Cincinnati, Ohio, 1993