Improved determination of trace anions in high purity waters by high-volume direct injection with the Dionex EG40 eluent generator

Importance of the topic

Trace-level assessment of anions in high-purity water is crucial for industries such as semiconductor manufacturing, power generation and pharmaceuticals, where ionic contaminants can compromise critical processes and product quality. Achieving accurate sub-µg/L detection demands methodologies that minimize contamination, reduce background noise and streamline analysis workflows.

Objectives and overview of the study

This work aims to demonstrate an improved approach for trace anion determination in ultrapure water through high-volume (1 mL) direct injection ion chromatography, leveraging the Thermo Scientific Dionex EG40 eluent generator to supply high-purity, carbonate-free KOH eluents and a Dionex IonPac AS15-5 μm column for efficient separation within 20 minutes.

Methodology

An online Dionex EG40 module electrochemically generates KOH eluents at concentrations up to 60 mM. A 1 mL sample is injected directly onto a 3 × 150 mm IonPac AS15-5 μm column under a gradient from 7 mM to 60 mM KOH at 0.7 mL/min and 30 °C. An ASRS ULTRA 2 mm suppressor in Gas-Assisted Recycle mode provides suppressed conductivity detection at 100 mA. Calibration standards in deionized water cover low-µg/L to ng/L levels, and method detection limits are calculated from seven replicates (99% confidence).

Used instrumentation

• Thermo Scientific Dionex EG40 Eluent Generator with EGC-KOH cartridge and degas unit
• Dionex GS50 Gradient Pump and CD25 Conductivity Detector (or ICS-5000+/Integrion HPIC system equivalent)
• Dionex IonPac AS15-5 μm analytical column (3 × 150 mm) with AG15-5 μm guard
• Dionex ASRS ULTRA 2 mm suppressor, Gas-Assisted Recycle mode
• Rheodyne injector with 1 mL PEEK sample loop
• PeakNet Chromatography Workstation

Main results and discussion

Method detection limits for eleven anions range from 0.04 µg/L (fluoride) to 0.83 µg/L (sulfate). Calibration curves exhibit r2 > 0.99. Baseline noise remains below 10 nS and shifts under 200 nS during gradients. Direct injection avoids concentrator columns, and the EG40 ensures stable carbonate-free eluents. Trace-level spikes of fluoride, acetate and formate in blanks were traced to point-of-use water system contamination.

Benefits and practical applications

• Eliminates need for external concentrator or sample pump
• Reduces water consumption and waste via Gas-Assisted Recycle suppressor mode
• Short run times (<20 min) with high peak efficiency
• Enhanced sensitivity and reproducibility at sub-µg/L levels
• Streamlined setup suitable for QA/QC and research laboratories

Future trends and possibilities

Advances may include integration of eluent generation and detection modules for turnkey systems, coupling with mass spectrometry for extended analyte coverage, and application of automated data processing with machine learning to enhance throughput and diagnostics. Further miniaturization and lower-volume loops may reduce sample requirements and broaden applicability to diverse water matrices.

Conclusion

The combination of the Dionex EG40 eluent generator and IonPac AS15-5 μm column with high-volume direct injection delivers robust, sensitive and efficient trace anion analysis in high-purity water. The method simplifies hardware requirements, lowers detection limits and supports rapid, reliable monitoring in critical industrial and research settings.

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