Analysis of Organic Acids in Beer by Ion-Exclusion Chromatography and Post-Column pH-Buffering Conductivity Detection

Significance of the Topic

Beer acidity significantly affects both sensory characteristics and microbial stability. Organic acids produced during fermentation contribute to sour, bitter, and salty flavor notes while also inhibiting spoilage organisms, making their precise quantification essential for quality control in brewing.

Objectives and Study Overview

This study presents an ion-exclusion chromatography (IEC) method with post-column pH buffering and conductivity detection for simultaneous analysis of key organic acids in beer. The goal was to optimize separation selectivity and detection sensitivity using Shimadzu’s Nexera Organic Acid Analysis System.

Methodology and Instrumentation Used

The method employs isocratic IEC with a 5 mM p-toluenesulfonic acid mobile phase. A post-column reagent (5 mM p-toluenesulfonic acid, 0.1 mM EDTA·4H₂O, 20 mM BIS-TRIS) continuously neutralizes the eluent to enhance conductivity detection of ionized acids. Separation is achieved on two serially connected Shim-pack SCR-102H columns (300 × 8 mm I.D., 7 μm) at 50 °C. Key parameters include a 0.8 mL/min eluent and reagent flow, 20 µL injections, and a total runtime of 35 min. Beer samples are degassed ultrasonically, filtered, diluted 1:10 with ultrapure water, and directly injected.

• Shimadzu Nexera Organic Acid Analysis System
• Shim-pack SCR-102H columns (300×8 mm, 7 μm) × 2 with guard column
• Post-column pH-buffering reagent addition module
• Conductivity detector (cell temperature 53 °C)
• Ultrasonic bath for sample degassing

Main Results and Discussion

Baseline separation was achieved for eight organic acids (citric, pyruvic, malic, succinic, lactic, formic, acetic, and pyroglutamic acids). Limits of detection ranged from 1 to 6 µM, retention time and peak area RSDs were below 1.7%, and calibration linearity exceeded R² = 0.9999. Analysis of five commercial beer samples revealed acid concentrations varying from below 0.3 mM up to 5.6 mM for citric acid and 5.1 mM for lactic acid. Implementation of the Shimadzu overlap injection function reduced analysis time by 13 minutes per run after the first injection without compromising resolution.

Benefits and Practical Applications

• High-resolution, sensitive simultaneous quantification of multiple organic acids.
• Robust precision and linearity support routine QA/QC in brewery and beverage laboratories.
• Overlap injection increases sample throughput, improving laboratory efficiency.

Future Trends and Applications

Emerging trends include faster column architectures and miniaturized systems for on-site analysis. Coupling IEC with mass spectrometry could offer structural confirmation of acids. Automated data processing and real-time monitoring will further enhance process control in brewing operations.

Conclusion

The developed IEC method with post-column pH buffering on the Shimadzu Nexera platform provides a reliable, efficient, and high-throughput solution for comprehensive organic acid profiling in beer. Its excellent resolution, sensitivity, and precision make it ideal for both research and quality assurance applications.

References

1. Anderson H.E., Santos I.C., Hildenbrand Z.L., Schug K.A. Analytica Chimica Acta 1085:1–20 (2019).
2. Shimadzu Application News No. 01-00171-EN – Nexera Organic Acid Analysis System and its Application.
3. Shimadzu Technical Report C190-E237A – High-Speed Analysis of Organic Acids Using Shim-pack Fast-OA and pH-Buffered Electrical Conductivity Detection.