QUANTITATIVE DETERMINATION OF GALLIC ACID AND TANNIC ACID FROM GALLNUT EXTRACT

Significance of the Topic

Oak gall extracts are rich in phenolic compounds, notably gallic acid and tannic acid, which exhibit antibacterial, antiviral, antifungal and anti-inflammatory properties. Their traditional use in medicine and modern interest in natural bioactive ingredients make reliable quantification methods essential for quality control and product development.

Objectives and Study Overview

This study aimed to develop and validate a high-performance liquid chromatography (HPLC) method for the simultaneous quantification of gallic acid and total tannic acid in a glycerin–water gallnut extract. The work focused on establishing detection limits, quantification limits, precision metrics and a robust analytical workflow suitable for complex sample matrices.

Methodology and Instrumentation

A reversed-phase HPLC method was implemented on an AZURA Analytical HPLC Plus system, comprising:

• P 6.1L HPG pump (up to 700 bar)
• Autosampler 3950
• Column thermostat CT 2.1 set at 30 °C
• DAD 6.1L diode array detector set to 280 nm
• Eurospher II 100-3 C18H column (150×3 mm)

The mobile phase used a binary gradient of:

• Eluent A: Water with 0.1% formic acid
• Eluent B: Acetonitrile–water (50:50, v/v) with 0.1% formic acid

Gradient profile ran from 95% A to 100% B over 5 minutes and back to initial conditions by 15 minutes. Flow rate was 1 mL/min. Sample preparation included dilution of the viscous extract (1:1000 with water), filtration through a 0.45 µm hydrophilic filter and injection volumes of 10 µL for gallic acid and 1 µL for total tannic acid.

Main Results and Discussion

Calibration curves for both analytes demonstrated linearity across the tested range. Method performance metrics were:

• Gallic acid LOD: 12 ng/mL; LOQ: 40 ng/mL
• Tannic acid (sum parameter) LOD: 120 ng/mL; LOQ: 400 ng/mL
• Repeatability (n=4): 1.94% RSD for gallic acid; 0.51% RSD for tannic acid

The dilution and filtration steps effectively addressed matrix viscosity, enabling direct injection without further extraction. Chromatograms showed well-resolved peaks and consistent retention times, confirming method robustness.

Benefits and Practical Applications

The developed HPLC approach offers a fast, accurate and reproducible protocol suitable for routine quality control of tannin-rich extracts. It eliminates time-consuming sample cleanup and delivers reliable quantification in complex glycerin–water matrices. Applications extend to pharmaceutical, cosmetic and nutraceutical product testing.

Future Trends and Potential Applications

Expected future developments include:

• Scaling the method to preparative chromatography for gallic acid isolation using fully aqueous eluents
• Integration with online sample preparation techniques to further reduce manual handling
• Extension of the method to quantify additional phenolic constituents in herbal extracts
• Automation in high-throughput quality control laboratories

Conclusion

The validated HPLC method provides a streamlined workflow for quantifying gallic acid and total tannic acid in oak gall extracts. Its sensitivity, precision and minimal sample preparation render it ideal for routine monitoring of bioactive phenolics in diverse industrial applications.

Reference

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