Determination of trace anions in high purity waters using a large-volume direct injection

Significance of the Topic

Trace-level anion analysis in high-purity water is critical in semiconductor manufacturing, power generation, electronics and nuclear industries to prevent corrosion and ensure component longevity. Sensitive monitoring of anions such as fluoride, chloride, sulfate and phosphate at sub-µg/L levels enables early detection of ionic contamination that can compromise process reliability and product quality.

Objectives and Study Overview

This study evaluates a Thermo Scientific™ Dionex™ ICS-6000 ion chromatography system with an EGC 500 KOH eluent generator and a Dionex™ IonPac™ AS28-Fast-4µm (2 × 150 mm) column using large-volume direct injection. The aim is to demonstrate a simplified workflow for the quantification of 11 inorganic and organic anions at trace levels in high-purity water without a concentrator column.

Methodology and Instrumentation

A gradient elution program (7 mM to 72 mM KOH) is applied to resolve weakly to strongly retained anions in a single 30 min run. Samples are injected directly (500 µL) using a large-loop PEEK tubing setup and suppressed conductivity detection with a Dionex™ ADRS 600 suppressor in recycle mode. Strict clean-room protocols, contaminant-free consumables and daily DI water conditioning ensure reliable trace-level performance.

Instrumentation Used:

• Thermo Scientific™ Dionex™ ICS-6000 HPIC system (DP Pump, EG Eluent Generator, CD Conductivity Detector)
• Dionex™ AS-AP Autosampler with 5 mL syringe and 8.5 mL buffer line
• Dionex™ EGC 500 KOH Eluent Generator Cartridge
• Dionex™ CR-ATC 600 Continuously Regenerated Anion Trap Column
• Dionex™ ADRS 600 Anion Suppressor (2 mm)
• Dionex™ IonPac™ AS28-Fast-4µm analytical (2 × 150 mm) and AG28-Fast-4µm guard (2 × 30 mm) columns

Main Results and Discussion

The AS28-Fast-4µm column provided enhanced resolution and peak efficiency compared to conventional IonPac AS15. Calibration over four levels (0.125–10 µg/L) yielded linearity (r2 > 0.98). Method detection limits (MDLs) ranged from 0.015 µg/L for nitrite to 0.313 µg/L for sulfate under direct-injection conditions. System blanks and DI water blanks identified low-level background contributions, particularly for fluoride, acetate and formate, highlighting the importance of rigorous rinsing and conditioning.

Benefits and Practical Applications of the Method

This approach eliminates the need for concentrator columns and additional pumps, reducing system complexity and maintenance. High capacity and selectivity enable large-volume injections without column overload. The method is readily applicable for routine monitoring of ultrapure water in semiconductor fabs, power plants and QA/QC laboratories.

Future Trends and Potential Applications

Advances in low-contamination materials and automated cleaning will further lower detection limits. Integration of real-time monitoring with AI-based data analysis can provide continuous process control. Expanding the method to other matrices (e.g., process chemicals, pharmaceutical water) and coupling with mass spectrometry can broaden analytical capabilities.

Conclusion

The combination of a high-capacity IonPac AS28-Fast-4µm column, online KOH eluent generation and large-volume direct injection on the Dionex ICS-6000 system offers a robust, sensitive and streamlined solution for trace anion determination in high-purity waters. Sub-µg/L detection limits, excellent linearity and reproducible results demonstrate suitability for critical industrial applications.

Reference

1. Thermo Scientific Dionex IonPac AS28-Fast-4µm Columns Product Manual, P/N 065675 Revision 02, February 2018.
2. Manali Aggrawal and Jeffrey Rohrer, “Improved determination of trace anions in high purity waters by high-volume direct injection with the Dionex EG40 eluent generator,” Thermo Scientific Application Update 142, 2001.
3. Thermo Fisher Scientific Technical Note 112, “Determination of trace anions in ultrapure water using capillary ion chromatography,” 2016.
4. Thermo Fisher Scientific, Product Manual for Eluent Generator Cartridges, Doc. 065018-07, 2019.
5. Thermo Fisher Scientific, Product Manual for Continuously Regenerated Trap Column (CR-TC), Doc. 079684-04, 2020.
6. Thermo Fisher Scientific Dionex ICS-6000 Ion Chromatography System Operator’s Manual, Doc. 22181-97002.