Analysis of Organic acids by the post-column pH buffering-electric conductivity detection method

Importance of the Topic

Organic acids serve as critical markers in biomass fermentation and biofuel production processes. Accurate, rapid quantification of these compounds—such as lactic, acetic, succinic, and citric acids—is essential for monitoring fermentation performance, optimizing yields, and ensuring product quality in both research and industrial settings.

Objectives and Study Overview

This application note demonstrates a robust method for the simultaneous analysis of nine common organic acids by ion-exclusion chromatography. Two column configurations are compared: a conventional Shim-pack SCR-102H setup and a high-throughput Shim-pack Fast-OA arrangement. The goal is to assess analysis speed, resolution, and reproducibility when using post-column pH buffering coupled with conductivity detection.

Methodology and Instrumentation

Used Instrumentation

• Chromatography System: Nexera™ Organic Acid Analysis System
• Columns:
  • Conventional: Two Shim-pack SCR-102H (300 × 8.0 mm I.D., 7 µm) with a 50 × 6.0 mm guard column
  • Fast: Three Shim-pack Fast-OA (100 × 7.8 mm I.D., 5 µm) with Fast-OA(G) pre-column (10 × 4.0 mm I.D.)
• Mobile Phase and pH Buffer: Reagents Kit for Organic Acid Analysis System (P/N 228-61465-91)
• Flow Rate: 1.0 mL/min
• Column Temperature: 40 °C
• Post-column Mixer: MR 20
• Injection Volume: 10 µL (glass vials, 1.5 mL)
• Detection: Conductivity detector with post-column pH buffering

Main Results and Discussion

• Separation of Nine Organic Acids: Phosphoric, citric, pyruvic, malic, succinic, lactic, formic, acetic, and propionic acids (each at 1000 mg/L).
• Conventional Mode Performance: Baseline resolution achieved within approximately 20 minutes, demonstrating high selectivity for structurally similar acids.
• Fast Mode Performance: Analysis time reduced by more than 50% (around 8–10 minutes) while maintaining adequate resolution and peak symmetry for quantitative work.
• Reproducibility: Retention time RSD below 0.5% and peak area RSD below 2% for both column setups, confirming method robustness.

Benefits and Practical Applications

• Accelerated Throughput: Fast-OA columns cut analysis times, enabling high-capacity screening of fermentation samples in QA/QC laboratories.
• Method Versatility: Applicable to a broad range of biomass-derived samples, including fermentation broths and process streams.
• Enhanced Data Quality: Post-column buffering ensures stable baseline conductivity and reliable quantification across a wide concentration range.

Future Trends and Opportunities

• Integration with Automated Sampling: Coupling fast-OA methods to autosamplers for 24/7 monitoring of large-scale fermentations.
• Hybrid Detection Strategies: Combining conductivity with mass spectrometry to expand the detectable acid profile and improve sensitivity.
• Microbore and Capillary Formats: Development of smaller ID columns to reduce solvent consumption and further increase throughput.

Conclusion

The post-column pH buffering and conductivity detection method using Shim-pack SCR-102H and Fast-OA columns offers a reliable, high-speed solution for organic acid analysis. The approach balances speed and resolution, meeting the stringent demands of biofuel and fermentation monitoring while ensuring reproducible, high-quality data.

Reference

Application News L588 (JP, ENG), Shimadzu Corporation, First Edition Dec. 2021, ERAS-1000-0285