Ionic liquid micellar extraction for quantitative determination of sesquiterpenic acids in Valerianae Radix

A series of hydrophilic 1-alkyl-3-methylimidazolium, tetraalkylammonium and pyrrolidinium-based ionic liquids (ILs) were investigated as extractants for the sample preparation and quantitative determination of valerenic and acetoxyvalerenic acids in Valerianae radix. The extraction outcome was monitored by means of HPLC and the results were compared with these obtained according to the well established methods such as European Pharmacopoeia 8 method and Soxhlet extraction (total extraction), both conducted with methanol as a solvent. The extractions were carried out both at room temperature and conventional heating conditions, and the influence of the anion (chloride, bromide, acetate, trifluoroacetate, thiocyanate, dicyanamide, tricyanomethanide, acesulfamate and saccharinate), type of cation, alkyl chain length in the imidazolium ion, concentration, temperature, extraction time, particle size of root, and solid-liquid ratio was investigated.

The results obtained showed that the extraction yield is strongly dependent on the cation type. The best outcome was obtained with ILs composed of cations capable to form micelles in aqueous solution, e.g. 1-decyl-3-methylimidazolium chloride {[C₁₀C₁im]Cl}. Further, the extraction was found to be highly dependent on the IL concentration with best outcome (same with the reference methods) at concentrations slightly higher than IL CMC. As a result, an improved protocol for quantification of sesquiterpenic acids in root of Valeriana officinalis L. (Caprifoliaceae) was developed. Compared to the conventional procedures, it ensures same extraction yield but excludes the toxic and flammable organic solvents, the latter being of a great importance from safety point of view.

Acknowledgement: The financial support from the Bulgarian Science Fund, Ministry of Education and Science (project DFNI T02/23) is greatly acknowledged by the authors.