Improved Determination of Trace Anions in High Purity Waters by High-Volume Direct Injection with the EG40

Importance of the Topic

Trace anion analysis in high-purity water is essential for quality assurance in semiconductor fabrication, power generation, and pharmaceutical processes. Detecting inorganic anions and low molecular weight organic acids at trace levels ensures system integrity and product quality.

Objectives and Study Overview

This study demonstrates a method combining an EG40 potassium hydroxide eluent generator with IonPac AS15-5µm (3×150 mm) column using high-volume direct injection. The aim is to achieve sub-µg/L detection limits without a concentrator column or extra sample pump, simplifying instrumentation and improving sensitivity.

Methodology and Used Instrumentation

The method uses high-volume direct injection of 1 mL sample loops into a suppressed conductivity system. A gradient from 7 to 60 mM KOH eluent is produced online by EG40 with EGC-KOH cartridge. Separation is achieved on the IonPac AS15-5µm column at 30 °C and 0.7 mL/min. An ASRS-ULTRA 2 mm suppressor in gas-assisted recycle mode provides low noise and stable baselines. Key instrumentation includes:

• DX-600 ion chromatography system with GS50 gradient pump and CD25 conductivity detector
• LC30 enclosure and Rheodyne 9126 PEEK injector
• IonPac AG15 guard and AS15 analytical columns
• EG40 eluent generator with EluGen EGC-KOH cartridge and gas-assisted regeneration kit
• PEEK tubing for sample loops and trap columns (ATC-1 and ATC trap)

Main Results and Discussion

The method achieves baseline noise below 10 nS and background conductivity around 1 µS. Detection limits (MDLs) for 11 anions range from 0.04 µg/L (fluoride) to 0.49 µg/L (acetate). Calibration is linear with r2 above 0.99 across ppb to ppt levels. A typical chromatogram shows separation of fluoride, glycolate, acetate, formate, chloride, nitrite, sulfate, oxalate, bromide, nitrate, and phosphate in under 20 minutes. Blank analysis highlights potential contamination from point-of-use water and emphasizes rigorous cleaning and high-purity reagents.

Benefits and Practical Applications

This approach eliminates the need for a concentrator column and additional valves, reducing system complexity, water usage, and waste. It delivers high throughput with robust reproducibility, low detection limits, and minimal baseline shifts, making it suitable for routine QA/QC in high-purity water monitoring.

Future Trends and Applications

Advances may include integration with mass spectrometry, further automation of sample handling, miniaturized inline sampling probes, and application of machine learning for chromatogram interpretation. Continuous improvements in eluent generation and suppressor technology will further enhance sensitivity and efficiency.

Conclusion

The described method provides a streamlined, sensitive, and reproducible protocol for trace anion determination in high-purity waters. Its simplified setup and low detection limits support critical monitoring applications across multiple industries.

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