Ionic liquids based microwave-assisted extraction of lichen compounds with quantitative spectrophotodensitometry analysis

Ionic liquids based extraction method has been applied to the effective extraction of norstictic acid, a common depsidone isolated from Pertusaria pseudocorallina, a crustose lichen. Five 1-alkyl-3-methylimidazolium ionic liquids (ILs) differing in composition of alkyl chain and anion were investigated for extraction efficiency. The extraction amount of norstictic acid was determined after recovery on HPTLC with a spectrophotodensitometer. The proposed approaches (IL-MAE and IL-heat extraction (IL-HE)) have been evaluated in comparison with usual solvents such as tetrahydrofuran in heat-reflux extraction and microwave-assisted extraction (MAE). The results indicated that both the characteristics of the alkyl chain and anion influenced the extraction of polyphenolic compounds. The sulfate-based ILs [C1mim][MSO4] and [C2mim][ESO4] presented the best extraction efficiency of norstictic acid. The reduction of the extraction times between HE and MAE (2 h–5 min) and a non-negligible ratio of norstictic acid in total extract (28%) supports the suitability of the proposed method. This approach was successfully applied to obtain additional compounds from other crustose lichens (Pertusaria amara and Ochrolechia parella).

Graphical abstractVarious lichen compounds were isolated with imidazolium derived ILs using microwave-assisted extraction or heat-extraction.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► IL-MAE and IL-HE of various crustose lichens were performed using various imidazolium derived ionic liquids. ► Sulfate-based ILs [C1mim][MSO4] and [C2mim][ESO4] presented the best extraction efficiency of lichen compounds. ► Important reduction of extraction time (5 min versus 2 h) was performed using MAE in comparison with HE.