Determination of organic acids in herbal beverages using a compact ion chromatography system coupled with mass spectrometry

Significance of the Topic

Herbal beverages contain plant-derived organic acids that influence flavor, quality, and potential health benefits such as detoxification and mineral chelation. Accurate profiling of these acids is essential for product standardization, quality control, and nutritional analysis.

Objectives and Study Overview

This study aimed to develop a streamlined method for the identification and quantification of key organic acids in herbal drinks by coupling a compact high-pressure ion chromatography (HPIC) system with a single quadrupole mass spectrometer (MS). The focus was on enhancing selectivity for co-eluting compounds and improving analytical confidence.

Methodology and Instrumentation

• Chromatography: Thermo Scientific Dionex Integrion HPIC with Dionex IonPac AS11-HC-4µm guard and analytical columns.
• Eluent: Continuously generated KOH gradient (1–60 mM) via Dionex EGC 500 and CR-ATC 600 trap column, with suppressed conductivity detection using AERS 500e suppressor.
• Mass Spectrometry: Thermo Scientific ISQ EC single quadrupole MS in negative electrospray ionization mode, operated in Full Scan and Single Ion Monitoring (SIM) to resolve co-eluting acids.
• Sample Preparation: Dilution, centrifugation, and 0.2 µm filtration of aloe, hawthorn/plum, and goji drinks using internal standard 13C4-succinate (m/z 121) at 100 µg/L.

Main Results and Discussion

The HPIC–CD/MS method effectively separated 13 organic acids under a single gradient without organic modifiers. Conductivity detection provided baseline separation for most analytes, while MS in SIM mode resolved co-eluting pairs (acetate/glycolate, malate/succinate, malonate/tartrate). MS-based limits of detection were lower for most acids (e.g., glycolate 1.58 µg/L) compared to conductivity, except for formate and citrate. Ion suppression between malate and succinate was observed at high concentrations but was compensated by the 13C4-succinate internal standard.

Benefits and Practical Applications

• Direct analysis without derivatization simplifies workflow and reduces labor.
• Dual detection ensures accurate quantification and confirms peak identity, enhancing method robustness in QA/QC settings.
• Suitable for routine monitoring of herbal beverage quality and for research on nutritional and functional properties.

Future Trends and Potential Applications

Advances may include high-resolution MS integration, automated sample throughput, and expanded compound libraries for comprehensive profiling of plant matrices. Optimization of ionization parameters and use of isotopically labeled standards can further improve sensitivity and accuracy.

Conclusion

A compact HPIC system coupled to a single quadrupole MS provides a robust, sensitive, and selective approach for profiling organic acids in herbal beverages. The dual detection strategy overcomes co-elution challenges and enhances analytical confidence for product quality assessment.

Reference

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