Determination of trace anions in basic solutions by single pass AutoNeutralization and ion chromatography

Significance of the Topic

In advanced electronics manufacturing, even trace anions in concentrated basic solutions can lead to corrosion, deposition defects and electrical shorts. Ion chromatography with suppressed conductivity detection is a preferred technique for sub-µg/L analysis. However, direct injection of strong bases often overloads columns, forcing dilution that degrades sensitivity. The Single Pass AutoNeutralization approach overcomes this by neutralizing the sample in-line without dilution, preserving ultratrace detection limits and streamlining sample preparation.

Objectives and Study Overview

This work evaluates the integration of Single Pass AutoNeutralization with high-pressure IC systems to achieve robust trace anion analysis in concentrated bases. Key aims include method qualification for linearity, detection limits, reproducibility and accuracy, and demonstration of applicability to semiconductor reagents and industrial hydroxides.

Methodology and Instrumentation

The method employs a Dionex ICS-5000+ HPIC or Integrion HPIC system configured for recycle or external water mode. Main steps are:

• Autosampler loads 100 µL of base sample into a loop
• Auxiliary pump delivers purified water through an anion trap column to rinse the sample into a 4 mm AERS 500 suppressor at 300–490 mA
• Strong base is neutralized in a single pass, exchanging sample cations for hydronium
• Neutralized trace anions are retained on a UTAC-LP2 concentrator column
• Anion separation on IonPac AG18-4 µm/AS18-4 µm columns with a KOH gradient generated by EGC 500 and CR-ATC trap
• Detection by suppressed conductivity using a 2 mm AERS 500 suppressor at 28 mA

Key Results and Discussion

Method qualification established:

• Linearity over calibration ranges (0–10 µg/L fluoride, 0–50 µg/L chloride, bromide, nitrite, nitrate, sulfate and 0–100 µg/L phosphate) with r2 > 0.995
• Detection limits below 1 µg/L for most anions; fluoride and sulfate limited by system blanks
• Peak area RSDs of 0.9–3.3 for seven replicates at lowest standard
• Retention time RSDs < 1
• Recovery of a mid-range check standard between 87 and 107

Application to real samples showed:

• Semiconductor grade TMAOH solutions spiked at 10–100 µg/L yielded recoveries of 78–86
• Reagentgrade NaOH (5–25 w/w ) injections exhibited proportional anion responses; co-elution affected fluoride accuracy
• ACS grade TBAOH contained high native levels of bromide, phosphate and sulfate
• Fluoride separation from acetate/formate improved on an AS28-4 µm column at the expense of longer runtime

Benefits and Practical Applications

This technique enables direct, undiluted analysis of strong bases, reducing sample handling and waste. It preserves low-level sensitivity for quality control of semiconductor reagents, industrial caustics and process streams. The simplified workflow minimizes consumables and improves throughput for QA/QC labs in electronics, chemicals and materials sectors.

Future Trends and Applications

Advances may include expanded use of high-capacity suppressors for other challenging matrices, integration with mass spectrometry for speciation, further automation of inline neutralization and calibration, and development of novel column chemistries for faster or higher-resolution separations. Enhanced software workflows and inline water purification will support fully unattended ultratrace analysis in production environments.

Conclusion

Single Pass AutoNeutralization combined with high-pressure ion chromatography delivers a robust, sensitive and accurate method for trace anion determination in concentrated basic samples. It eliminates sample dilution, maintains ultratrace detection limits and streamlines QA/QC workflows in demanding industrial applications.

Reference

1 Thermo Fisher Scientific Application Note 72481 Determination of trace anions in basic solutions by single pass AutoNeutralization and ion chromatography
2 Thermo Fisher Scientific Application Note 93 Determination of trace anions in concentrated bases using AutoNeutralization Pretreatment and Ion Chromatography 1994
3 Thermo Fisher Scientific Application Note 94 Determination of trace cations in concentrated acids using AutoNeutralization Pretreatment and Ion Chromatography 2004
4 Thermo Fisher Scientific Application Update 159 Determination of volcanic gases as anions in caustic solutions using AutoNeutralization Automated Dilutions and RFIC 2007
5 Rose A and Voelker P Determination of trace anions in concentrated caustics using single-pass neutralization pretreatment and IC FL90024-EN Thermo Fisher Scientific 2014
6 ASTM D1193 Standard specification for reagent water ASTM International
7 Thermo Fisher Scientific Product Manuals for EGC 500, CR-ATC 500, ASRN II, AERS 500, IonPac AS18-4 µm, ICS-5000+ and AS-AP Autosampler