Determination of phenolic compounds in aromatic plants by RP-HPLC and GC-MS

It is well known that phenolic compounds are constituents of many plants and herbs, and they have attracted a great deal of public and scientific interest because of their health-promoting effects as antioxidants. Five plants, Vitex agnus-castus (Verbenaceae), Origanum dictamnus (Lamiaceae), Teucrium polium (Lamiaceae), Lavandula vera (Lamiaceae) and Lippia triphylla (Verbenaceae), were examined in order to determine their phenolic composition. Reversed phase high performance liquid chromatography was employed for the identification and quantification of phenolic compounds. Gas chromatography–mass spectometry(GC-MS) was also used for identification of phenolic compounds after silylation. Analysis of the non-volatile and thermolabile phenolic compounds by GC-MS presupposes their conversion into volatile and thermotolerant derivatives. The derivatization process was optimized against reagents, temperature and reaction time. A large excess of N,O-bis(trimethylsilyl)trifluoroacetamide containing trimethylchlorosilane proved to be the best derivatization reagent to convert analytes into volatile trimethylsilyl derivatives. The most abundant phenolic compounds detected were caffeic acid (0.12–0.93 mg 100 g−1 dry sample), ferulic acid (0.34–1.52 mg 100 g−1 dry sample), and (+)-catechin (0.22–0.43 mg 100 g−1 dry sample).