Determination of trace anions in organic solvents using matrix elimination and preconcentration

Importance of the Topic

In semiconductor and electronics manufacturing, trace anion contaminants in organic solvents can cause defects, corrosion, and yield losses. As device geometries shrink, even ng/L–µg/L levels of anions like chloride, sulfate, nitrate, and phosphate become critical. Reliable, low‐level anion analysis in solvents such as isopropanol, methanol, acetone, and N-methyl-2-pyrrolidone (NMP) is essential for quality control and waste minimization.

Objectives and Study Overview

This work presents an automated, high-sensitivity method to determine trace anions in organic solvents. It updates a previous manual procedure (Application Note 85) by integrating matrix elimination, preconcentration, and reagent-free eluent generation to achieve lower detection limits, improved consistency, and reduced operator effort.

Methodology and Instrumentation

The approach uses a two‐system configuration on a Dionex ICS-3000 RFIC platform:

• System 2 (Sample Preparation): A Dionex AS-HV high-volume autosampler in pull mode loads 5 mL of solvent through an IonPac ATC-HC trap column (9 × 75 mm) at 2.0 mL/min, eliminating the solvent matrix to waste.
• System 1 (Analytical Separation): An IonPac UTAC-ULP1 concentrator (5 × 23 mm) traps the retained anions, which are then eluted onto an IonPac AG18/AS18 column pair (2 × 50 mm + 2 × 250 mm) using electrolytically generated KOH gradient from 22 to 65 mM. Suppressed conductivity detection is performed with an ASRS ULTRA II suppressor and a CRD 200 carbonate removal device.
• Eluent Generation: A Dionex EG Eluent Generator produces consistent potassium hydroxide eluents, eliminating manual preparation and CO₂ interference.

Key instrumentation and components:

• Dionex ICS-3000 RFIC with DP dual pump, EG eluent generator, and DC detector module
• Dionex AS-HV autosampler with internal peristaltic pump
• IonPac ATC-HC trap, UTAC-ULP1 concentrator, AG18/AS18 analytical columns, ASRS ULTRA II suppressor, CRD 200 device

Main Results and Discussion

Method performance was evaluated for chloride, sulfate, nitrate, and phosphate in water and four solvents:

• Linearity: r² > 0.999 over 0.1–50 µg/L (nine‐point calibration).
• Noise: <3 nS; baseline <2 µS.
• MDLs: 0.11–0.45 µg/L (4×–5× lower than previous method; 100×–2 800× below SEMI specifications).
• Precision: <0.6% RSD retention time; peak area RSD <1.1% (except phosphate at 2.7%).
• Recoveries: 98.9–101.2% in water; 92.5–106.4% in solvents (exception: nitrate recovery in acetone was 19%, cause unknown).
• Analysis time: 44–50 min per sample with potential overlap mode to reduce total runtime.

Benefits and Practical Applications

This automated matrix elimination and preconcentration method offers:

• Lower sample volume (2 mL injection) and reduced solvent use.
• Reagent-free eluent generation, improving reproducibility and reducing labor.
• MDLs far exceeding industry requirements for SEMI Grade specifications.
• Fully automated workflow, freeing operator time and minimizing carryover.
• Compatibility with routine QC in semiconductor, electronics, and chemical manufacturing.

Future Trends and Opportunities

Advances to watch include:

• Integration with high-resolution mass spectrometry for enhanced selectivity.
• Microfluidic and capillary IC formats to further reduce sample and reagent consumption.
• Expanded analyte panels covering organic acids and fluorinated anions.
• Real-time inline monitoring of solvent purity in manufacturing lines.

Conclusion

The updated method combines RFIC reagent-free eluent generation with automated matrix elimination and preconcentration to deliver highly sensitive, reproducible anion analysis in organic solvents. It meets or exceeds SEMI specifications, reduces operator workload, and provides a robust tool for quality control in high-purity applications.

References

1. Thermo Fisher Scientific. Determination of Trace Anions in Solvent; Application Note 85, LPN 0482-03, 2004.
2. Thermo Fisher Scientific. Eluent Preparation for High-Performance Anion-Exchange Chromatography with Pulsed Amperometric Detection; Technical Note 71, LPN 1932, 2007.
3. Thermo Fisher Scientific. Improved Determination of Trace Anions in High Purity Waters by High-Volume Direct Injection with the EG40; Application Update 142, LPN 1291, 2001.
4. Thermo Fisher Scientific. ICS-3000 Ion Chromatography System Installation Instructions; Doc. 065032, 2005.
5. Thermo Fisher Scientific. ICS-3000 Ion Chromatography System Operator’s Manual; Doc. 065031, 2005.
6. Thermo Fisher Scientific. Product Manual for IonPac ATC-3 and ATC-HC; Doc. 032697, 2002.
7. Thermo Fisher Scientific. Product Manual for Anion Self-Regenerating Suppressor ULTRA II; Doc. 031956, 2005.
8. Thermo Fisher Scientific. Product Manual for Carbonate Removal Device CRD200; Doc. 065068, 2007.
9. Thermo Fisher Scientific. Product Manual for IonPac AG18 Guard and AS18 Analytical Columns; Doc. 031878, 2005.
10. Thermo Fisher Scientific. Product Manual for IonPac UTAC Concentrator; Doc. 065091, 2005.
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12. Thermo Fisher Scientific. Installing Chromeleon with a Dionex Ion Chromatograph; Doc. 031883, 2005.
13. Thermo Fisher Scientific. Reducing Carbonate Interference in Anion Determinations with the Carbonate Removal Device; Technical Note 62, LPN 1765, 2006.
14. SEMI. SEMI C10-0305 Guide for Determination of Method Detection Limits; 2005.
15. SEMI. SEMI C41-0705 Specifications and Guidelines for 2-Propanol; 2005.
16. SEMI. SEMI C19-0301 Specification for Acetone; 2001.
17. SEMI. SEMI C31-0301 Specification for Methanol; 2001.
18. SEMI. SEMI C33-0301 Specification for N-Methyl-2-Pyrrolidone; 2001.