Analysis of traditional Chinese medicines with the Agilent 1200 Series evaporative light scattering detector

Significance of the topic

Traditional Chinese Medicines (TCMs) contain non-chromophoric bioactive compounds that evade detection by conventional UV detectors. The adoption of evaporative light scattering detection (ELSD) enables universal detection of analytes less volatile than the mobile phase. Implementing ELSD for quality control aligns with requirements of the Chinese Pharmacopoeia and addresses challenges in monitoring key herbal constituents.

Objectives and study overview

This application note illustrates two analytical methods developed on the Agilent 1200 Series Rapid Resolution LC system equipped with ELSD, targeting:

• Quantitative determination of flavonoids in Ginkgo biloba L. extracts
• Analysis of astragaloside in Radix Astragali (Huangqi)

Methodology and instrumentation

Both methods employed a gradient HPLC protocol on an Agilent 1200 RRLC system comprising:

• Binary pump SL with vacuum degasser
• Thermostatted column compartment (40 °C)
• High-performance autosampler
• Diode array detector (for complementary UV monitoring)
• Evaporative light scattering detector (40 °C, 3.5 bar, gain 7, 1 s filter)
• ZORBAX XDB-C18 column (3.0 × 50 mm, 1.8 µm) or comparable
• Agilent ChemStation software for data acquisition

Sample preparation involved ultrasonic extraction in methanol, filtration, and injection of 20 µL.
Gradient programs were optimized to separate target analytes within 20–35 min, using water–acetonitrile or water–tetrahydrofuran/methanol mobile phases at 0.7 mL/min.

Main results and discussion

• ELSD vs. UV comparison revealed negligible UV response at 254 nm and weak at 210 nm for Ginkgo flavonoids, underscoring ELSD necessity.
• Gradient HPLC-ELSD achieved baseline separation of four major flavonoids (bilobalide, ginkgolides C, A, B) and astragaloside from matrix components.
• Calibration curves displayed high linearity (R² > 0.998) within defined ranges; ELSD response modeled as A = a·mᵇ, with linear segments for quantitation.
• Detection limits ranged from 12.5 ng (ginkgolide A) to 30 ng (ginkgolide C) under optimized ELSD settings.
• Monitoring complementary UV channels throughout gradient runs prevents undetected elution and system contamination.

Benefits and practical applications of the method

• Universal detection of non-volatilizable compounds without derivatization
• Compatibility with gradient separations and complex herbal matrices
• Compliance with Chinese Pharmacopoeia ELSD requirements for TCM analysis
• Enhanced sensitivity and stable baselines in absence of chromophores
• Streamlined quality control workflows for research and manufacturing laboratories

Future trends and applications

Continuing research aims to refine ELSD response models based on particle size dynamics and to extend the linear quantitation range. Integration with mass spectrometry and advanced data processing may further enhance detection specificity and throughput for herbal and complex sample analysis.

Conclusion

The Agilent 1200 Series RRLC coupled with ELSD provides a robust, sensitive, and universal platform for quantifying key non-UV-absorbing constituents in traditional Chinese medicines. The validated methods satisfy pharmacopeial standards and support reliable quality control of Ginkgo biloba and Radix Astragali extracts.

Reference

• Pharmacopoeia of the People’s Republic of China, 2005.
• Qi L-W, et al. Quality evaluation of Radix Astragali through simultaneous determination of six isoflavonoids and four saponins by HPLC-DAD and ELSD. J Chromatogr A, 1134, 162–169 (2006).
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• Su H, et al. Determination of jujuboside A in Ziziphi Spinosae mixture by HPLC-ELSD. J Mod Food Pharm, 17(6), 35–37 (2007).