Determination of trace anions in high-purity waters by ion chromatography with the Dionex IonPac AS17 column using high-volume direct injectio

Significance of the topic

Trace anionic contaminants in high-purity waters can originate from cleaning agents, adhesives, oils and other sources and pose serious risks for corrosion in microelectronic circuits, pharmaceutical processes and analytical assays. Sensitive, reliable detection of inorganic anions, low-molecular-weight organic acids, and polymerization-related species such as acrylate and phthalate is therefore critical for quality assurance in industry and research.

Objectives and overview of the study

This study presents an ion chromatographic method using the Dionex IonPac AS17 column and high-volume (1 mL) direct injection to quantify trace levels (sub-µg/L) of common inorganic and organic anions in ultrapure water. Two gradient protocols (27 min and 41 min) are optimized to balance sample throughput and resolution across fifteen target anions. Performance metrics including detection limits, linearity and blank response are evaluated.

Instrumentation used

• Thermo Scientific Dionex DX-600 or ICS-5000+ HPIC or Integrion HPIC system
• GS50 Gradient Pump and LC30 oven (30 °C)
• CD25 Conductivity Detector with ASRS™ ULTRA 2 mm suppressor in gas-assisted recycle mode
• Dionex EG40 Eluent Generator with EGC-KOH cartridge
• IonPac AG17 guard column (2 × 50 mm), IonPac AS17 analytical column (2 × 250 mm), and ATC-3 trap column (9 × 24 mm)
• PEEK tubing loop (0.030 in., 1000 µL) for high-volume injection

Methodology

The method employs carbonate-free KOH gradients generated in-line by the EG40 eluent generator. A 5 min equilibration at a low initial KOH concentration elutes weakly retained ions (fluoride, acetate, formate) followed by a stepped gradient to separate strongly retained species (sulfate, phosphate, phthalate). Two protocols are used: Method 1 (27 min) for rapid analysis of well-known samples, and Method 2 (41 min) for enhanced separation of analytes at disparate concentrations. Standards are prepared from 1000 mg/L stocks and diluted to low-µg/L for calibration. Blanks are monitored to ensure a stable background (<10 nS noise, <200 nS drift).

Main results and discussion

The method achieved baseline separation of fifteen anions with method detection limits (MDLs) ranging from 0.04 µg/L (fluoride) to 1.1 µg/L (acetate). Calibration curves displayed linearity (r² > 0.99) over low-ppb ranges. Blanks showed only carbonate and an unidentified small peak, confirming minimal contamination. Gas-assisted recycle operation of the suppressor reduced noise by 4–10× and eliminated the need for external regenerant water. Column and suppressor stability were maintained by periodic trap column regeneration and inline degassing.

Benefits and practical applications of the method

• Direct injection of 1 mL sample simplifies workflow, avoiding concentrator columns and valves
• In-line KOH generation and gas-assisted suppression minimize baseline drift and water waste
• Low MDLs support quality control in microelectronics, pharmaceutical and environmental laboratories
• Gradient flexibility allows rapid screening or detailed analysis depending on sample complexity

Future trends and possibilities for application

Advances in eluent generator technology, trap column materials (e.g., ATC-HC), and miniaturized IC systems will further lower detection limits and reduce maintenance. Integration with mass spectrometric detectors could expand specificity for emerging contaminants. Automation and on-site monitoring platforms may enable continuous water quality surveillance in critical processes.

Conclusion

This application note demonstrates a robust, sensitive ion chromatography method using high-volume direct injection and the Dionex IonPac AS17 column for comprehensive trace anion analysis in high-purity waters. The approach delivers low detection limits, high throughput and minimal baseline noise, meeting stringent requirements for industrial and research workflows.

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