Determination of trace anions in concentrated glycolic acid

Significance of the topic

The presence of trace chloride and sulfate in concentrated glycolic acid poses a serious risk of corrosion in electronic soldering flux applications. Accurate measurement of these anions at sub-mg/L levels is therefore critical for quality assurance and product safety.

Objectives and Study Overview

This study aimed to develop a sensitive and robust ion chromatography method for determination of trace chloride and sulfate in 0.7 to 17.5 percent (v/v) glycolic acid. Key goals were to overcome interference from the high glycolate matrix and to achieve reliable detection limits in the low microgram per liter range.

Methodology and Instrumentation

The analytical approach combined an ion exclusion pre-separation with a subsequent anion exchange concentration and separation. Main system components included

• Thermo Scientific DX-500 (or ICS-5000+) with GP50 pump and CD20 conductivity detector
• PEEK Rheodyne sample valve and pressurized reservoir for loading
• Dionex ICE-AS6 ion exclusion column for matrix removal
• Dionex AG9-HC concentrator column (4 mm) and AS9-HC microbore analytical column set (2 mm)
• Suppressed conductivity detection using ASRS-ULTRA in external water mode

Key operating parameters:

• Ion exclusion eluent: deionized water at 0.55 mL/min
• Sample loop volume: 750 µL; loading via 5 psi helium
• Concentrator eluent: 8 mM carbonate/1.5 mM hydroxide at 0.25 mL/min
• Isocratic IC separation on AS9-HC microbore column

Main Results and Discussion

System blanks in deionized water were reduced to 30 µg/L sulfate after extended rinsing. Calibration by standard additions in the diluted glycolic acid matrix yielded linear responses for chloride and sulfate with r2 above 0.999. Spike recoveries ranged from 105 to 112 percent over test levels of 20 µg/L chloride and 500 µg/L sulfate. Method detection limits were determined as approximately 2 µg/L for chloride and 20 µg/L for sulfate. Precision for seven replicate analyses of 0.7 percent glycolic acid showed relative standard deviations below 10 percent.

Benefits and Practical Applications

This two-stage separation strategy effectively isolates trace anions from a dominating glycolate background without extensive sample dilution. Microbore columns enhance sensitivity and reduce eluent consumption. The method provides routine analysis capability for corrosion-critical flux materials and can be implemented in QA/QC and research laboratories.

Future Trends and Applications

Advances may include use of gradient eluent profiles on hydroxide-selective columns to further improve resolution, coupling with mass spectrometry for enhanced identification, and development of automated microfluidic sample pretreatment modules. Adaptation to other challenging weak acid matrices and continuous monitoring formats will broaden applicability.

Conclusion

The presented ion exclusion pre-separation coupled with anion exchange concentration and microbore IC provides a sensitive, robust, and reproducible method for quantifying trace chloride and sulfate in concentrated glycolic acid. Detection limits in the low µg/L range and high spike recoveries demonstrate suitability for demanding corrosion control applications.

References

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5. J Weiss Ion Chromatography 2nd Ed VCH Weinheim 1995 209–210