Determination of Anions and Organic Acids in Brewed Coffee Samples Using Capillary IC

Importance of the Topic

Coffee acidity and inorganic anion content critically influence flavor, aroma and bean quality in brewed coffee. Monitoring organic acids and anions helps differentiate Arabica and Robusta varieties, assess cherry maturity and roasting extent, and detect potential adulteration.

Objectives and Study Overview

This application brief describes the rapid separation and quantification of inorganic anions and organic acid anions in both caffeinated and decaffeinated brewed coffee using capillary ion chromatography. The study aims to achieve high resolution within 20 minutes, low reagent consumption, and improved mass sensitivity.

Methodology and Instrumentation

The analysis employs a Thermo Scientific Dionex ICS-5000 capillary RFIC system with:

• Dionex IonSwift MAX-100 capillary anion-exchange column (0.25 × 250 mm) with guard
• In-line electrolytic generation of potassium hydroxide eluent
• Dionex ACES Capillary Electrolytic Suppressor in recycle mode for suppressed conductivity detection
• Gradient elution from 0.1 mM to 65 mM KOH at 12 µL/min

Samples were prepared by diluting brewed coffee at 1:50 in deionized water, injecting 0.4 µL, and maintaining the column at 30 °C.

Main Results and Discussion

In caffeinated coffee, pronounced peaks for quinate, formate, malate, citrate, chloride and phosphate were observed. Decaffeinated samples showed reduced quinate, lactate and malate, with near absence of formate and citrate. These profiles align with known differences between Arabica (higher malate and quinate) and Robusta beans, and reflect the impact of decaffeination and roasting on volatile organic acids.

Benefits and Practical Applications

• Rapid profiling of coffee acidity and inorganic anions within 20 min
• Ultra-low eluent and water consumption (12 µL/min, 15 mL/day)
• Enhanced mass sensitivity and resolution for quality control
• Tools for authentication, maturity monitoring and roast level assessment

Future Trends and Opportunities

Advancements in capillary IC will drive further miniaturization, integration with mass spectrometry for structural insights, and real-time monitoring of coffee processing. Emerging suppressor technologies and novel monolithic columns will reduce analysis time and expand detectable analyte range.

Conclusion

Capillary RFIC with the Dionex IonSwift MAX-100 column provides a robust, sensitive and eco-friendly approach for comprehensive anion and organic acid analysis in brewed coffee. This method supports quality assurance, varietal differentiation and process optimization.

Reference

• Moura SC, Germer SPM, Anjos VDA, Mori EEM, Mattoso LHC, Firmino A, Nascimento CJF Evaluation of Physical, Chemical and Sensorial Characteristics of Arabica and Canephora (Robusta) Coffee Blends Proceedings of the Association for Science and Information on Coffee, 22nd Conference Campinas Brazil September 2008
• Roger WJ, Michaux S, Bastin M, Bucheli P Changes to the Content of Sugars, Sugar Alcohols, Myo-Inositol, Carboxylic Acids and Inorganic Anions in Developing Grains from Different Varieties of Robusta (Coffea canephora) and Arabica (C Coffea arabica) Coffees Plant Sci Amsterdam Neth 1999 149 115–123
• Galli V, Barbas C Capillary Electrophoresis for the Analysis of Short-Chain Organic Acids in Coffee J Chromatogr A 2004 1032 299–304