The determination of organic acids using suppressed conductivity ion chromatography

Significance of the Topic

• Short-chain carboxylic acids occur widely in environmental waters, beverages and physiological fluids and serve as important biochemical intermediates.
• Accurate determination of these organic acids is challenged by coexisting inorganic anions and the water dip in suppressed conductivity ion chromatography.

Study Objectives and Overview

This work presents a high-resolution ion chromatography method to separate four organic acids—formic, acetic, propionic and oxalic—from seven common inorganic anions using a Shimadzu modular IC system equipped with an electrolytically regenerated suppressor. The aim is to achieve clear resolution, reproducibility and accurate quantification even in complex water matrices.

Methodology and Instrumentation

The separation was conducted under the following conditions:

• Column: Shodex IC SI-52 4E (4 × 250 mm) with Shodex SI-90G guard column.
• Eluent: 5.4 mM sodium carbonate prepared from a 0.18 M stock solution.
• Flow rate: 0.8 mL/min at 45 °C.
• Injection volume: 20 µL; backpressure ~1450 psi.
• Detection: suppressed conductivity at 60 mA in recycle mode, background conductance ~29 µS/cm, noise <3 nS/cm.

Key system components included:

• CBM-40 lite controller, DGU-403 degasser, LC-20Ai pump with rinse kit.
• SIL-20AC autosampler with inert kit, CTO-40S column oven, suppressor installation kit.
• CDD-10Avp conductivity detector, ICDS-40A electrodialytic suppressor starter kit.

Main Results and Discussion

The method achieved full baseline separation of the four organic acids ahead of the water dip and fluoride peak, with clear resolution from seven inorganic anions. Precision studies using mixed standards showed retention time RSDs and peak area RSDs below 1% across eight injections. Recovery experiments in lake and tap water spiked at 2 ppm yielded recoveries between 91.8% and 102.8%. Linearity was demonstrated over 1–10 ppm for all organic acids with correlation coefficients exceeding 0.999.

Benefits and Practical Applications

• High resolution minimizes overlap with inorganic anions and water dip interference.
• Electrolytically regenerated suppression ensures stable background and low noise.
• Robust precision and accuracy support environmental, beverage and biofluid analysis.

Future Trends and Possibilities

• Integration with mass spectrometric detection for increased sensitivity and structural confirmation.
• Automation of sample preparation for high-throughput monitoring in environmental and clinical settings.
• Development of mixed eluent systems to extend separation to a broader range of organic acids and anions.

Conclusion

The described high-resolution ion chromatography method on a Shimadzu modular system with electrolytic suppression delivers reliable, reproducible separation and quantification of short-chain organic acids in the presence of common inorganic anions, meeting the demands of environmental and industrial analysis.