Characterization of European Ash Leaves by HPTLC and UHPLC-UV-MS

Reviewed: Kiss AK, Michalak B, Patyra A, Majdan M. UHPLC‐DAD‐ESI‐MS/MS and HPTLC profiling of ash leaf samples from different commercial and natural sources and their in vitro effects on mediators of inflammation. Phytochem Anal. 2019; doi: 10.1002/pca.2866. [Epub ahead of print]

Keywords: Adulteration, European ash, Fraxinus excelsior, Fraxinus ornus, HPTLC, manna ash, UHPLC-UV-MS/MS

European ash (Fraxinus excelsior, Oleaceae) leaves are used internally to treat rheumatism, arthritis, gout, fever, to increase diuresis, and externally as a wound-healing agent.¹ Ash leaves are predominantly administered as an herbal tea. The European Pharmacopoeia lists two species that may be used interchangeably, European ash and narrow-leafed ash (F. angustifolia).² The leaf contains 2.5-4.5% hydroxycinnamic acids and 0.6-2.2% flavonoids.¹ However, detailed information on its minor constituents is not available.

For this investigation, two authentic European ash leaf samples, and five commercial products (from the Austrian, French, Polish, and Portuguese markets) labeled to contain ash leaves were analyzed by high-performance thin-layer chromatography (HPTLC) and ultra-high-performance liquid chromatography with diode array and mass-spectrometric detection (UHPLC-UV[DAD]-MS/MS). Sixty-four compounds were fully or partly identified using the UHPLC-UV[DAD]-MS/MS analysis, including hydroxycinnamic and other phenolic acids, flavonoids, iridoids, and lignans. Based on the UHPLC-UV chromatograms provided by the authors, major compounds include verbascoside, 5-O-caffeoylquinic acid, ligstroside, rutin, oleuropein, and oleacteoside.

Ash leaf fingerprints varied substantially, especially in the quantitative composition. The commercial product from Austria, labeled to contain European ash, exhibited a number of additional compounds in the HPTLC and UHPLC-UV fingerprints. Two of these peaks were assigned to aesculetin glycosides, which are coumarins known from the leaves of manna ash (F. ornus). These coumarins were very distinct in the HPTLC analysis under UV light at 365 nm after spraying with diphenylboric acid aminoethyl ester reagent.

Comment: The publication details a thorough investigation of European ash leaves, and provides useful information on the chemical composition of the leaves, and the differences in leaf materials from different origins. The variability in the chemical fingerprints emphasizes the importance of having a large number of authentic samples from various origins to establish identification criteria.

Both the HPTLC and UHPLC-UV[DAD]-MS approach appear to be suitable for the identification of European ask leaf, and are considered to be helpful methods in the quality control of this herbal medicine.

References

1. Heise EM, Wichtl M, Loew D. Fraxini folium. In: Blaschek W, ed. Wichtl -Teedrogen und Phytopharmaka. Stuttgart, Germany: Wissenschaftliche Verlagsgesellschaft mbH; 2016: 267-268.
2. Committee on Herbal Medicinal Products (HMPC). Assessment report on Fraxinus excelsior L. or Fraxinus angustifolia Vahl, folium. London, United Kingdom: European Medicines Agency; 2012. Available at: https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-fraxinus-excelsior-l-fraxinus-angustifolia-vahl-folium_en.pdf. Accessed November 1, 2019.