Determination of Organic Acids in Beer Samples Using a High-Pressure Ion Chromatography System

Importance of the Topic

Beer is a complex sample matrix containing proteins, carbohydrates, inorganic ions, organic acids and ethanol. Accurate profiling of organic acids is essential for quality control, flavour optimization and detection of microbial spoilage in beer production.

Objectives and Study Overview

This technical note demonstrates the use of a 4 µm resin anion-exchange column (Dionex IonPac AS11-HC-4µm) combined with a high-pressure ion chromatography system (Dionex ICS-5000+ HPIC). The goals are to achieve high-resolution separation of organic acids and inorganic anions in beer and to compare performance with a 9 µm particle column format, as well as to explore selectivity adjustments using methanol modifiers.

Applied Methodology and Instrumentation

• Sample preparation: degassing by vacuum filtration with ultrasonic agitation, five-fold dilution and 0.20 µm syringe filtration.
• Eluent: electrolytically generated potassium hydroxide gradient (1–60 mM) with optional methanol modifier (2–20%).
• Columns: Dionex IonPac AS11-HC-4µm (4 × 250 mm and 2 × 250 mm) with guard columns.
• System configuration: Thermo Scientific Dionex ICS-5000+ HPIC with SP/DP pump, EG eluent generator, high-pressure degasser, autosampler and Chromeleon CDS.
• Detection: suppressed conductivity using AERS/ASRS suppressors in recycle or external water mode.

Main Results and Discussion

• The 4 µm column delivered 40–50 % higher resolution than a 9 µm column, enabling baseline separation of 40 analytes within 45 min at 0.38 mL/min.
• Critical peak pairs such as lactate/acetate and phosphate/phthalate showed resolution improvements from Rs ≈ 1.2 to Rs > 1.9.
• Methanol addition modified column selectivity, reversing elution order and resolving coeluting species like succinate and malate.
• Analysis of U.S. lager beers revealed distinct organic acid profiles, with variations in chloride, phosphate, citrate, pyruvate and sulfate reflecting brewing ingredient choices and processes.
• Spiked sample testing confirmed the method’s ability to detect spoilage markers (for example, butyrate) in complex beer matrices.

Benefits and Practical Applications of the Method

• High resolution and capacity for complex beer samples.
• Improved signal-to-noise and quantitation accuracy from smaller particle size.
• Adjustable selectivity through organic modifiers for targeted analyte separation.
• Consistent performance across column formats (4 mm, 2 mm and capillary) on HPIC platforms.
• Ideal for routine QA/QC, research and industrial beverage analysis.

Future Trends and Applications

• Adoption of capillary column formats to reduce solvent consumption and enhance sensitivity.
• Coupling with mass spectrometry for structural confirmation of unknown acids.
• Automation of sample preparation and data processing for high-throughput brewery quality control.
• Development of advanced stationary phases for isomeric organic acid separation.
• Extension of the approach to other fermented beverages and food quality monitoring.

Conclusion

The integration of a 4 µm AS11-HC column with a high-pressure IC system delivers superior separation efficiency, selectivity and operational robustness for organic acid analysis in beer, enhancing quality control and research capabilities.

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