Proposal for a standardised method for the identification of essential oils by HPTLC

The European Pharmacopoeia (Ph. Eur.), includes both individual monographs on essential oils and a general monograph that covers all essential oils for pharmaceutical use, whether covered by an individual monograph or not. The individual monographs generally describe gas chromatography as a first identification test, while thin-layer chromatography (TLC) and high-performance thin-layer chromatography (HPTLC) methods are included in the second identification series. To comply with Ph. Eur. general chapter 2.8.25. High-performance thin-layer chromatography of herbal drugs and herbal drug preparations, HPTLC parameters must be standardised. Currently, 18 of the 32 monographs on essential oils feature the same TLC/HPTLC method, but differ in terms of the other conditions described. A single, standardised chromatographic system with a system suitability test (SST) and intensity markers for all 32 essential oils covered by individual monographs would be desirable, particularly for pharmacies and other users that cannot perform gas chromatography for financial reasons. To this end, this paper describes the development of a general HPTLC method for the identification of essential oils in compliance with general chapter 2.8.25. The method proposes the use of ethyl acetate, toluene (5:95 V/V) as mobile phase, isoeugenol/isoeugenyl acetate for the SST, and a combination of one alcohol (either borneol or linalool) and one ester (either linalyl acetate or bornyl acetate) as intensity markers.