Application of different preparation techniques for extraction of phenolic antioxidants from lemon balm (Melissa officinalis) before HPLC analysis

Four different preparation techniques [SPE (Solid phase extraction) in off-line and on-line modes, PSE (Pressurized solvent extraction) and SFE (Supercritical fluid extraction)] were tested for the isolation of some phenolic compounds from Mellissa officinalis. Solid phase extraction methods using the hydrophilic-lipophilic sorbent (OASIS HLB) was used in off-line mode for clean-up of the water extract of medical plants. A generic SPE method was slightly modified, both washing and elution steps were optimized. The contents of methanol for both steps were recommended. Extraction recoveries for all analyzed compounds were about 100% with RSD values in the range 1.1-2.7%. On-line SPE has also been applied for phenolic compounds isolation. Pressurized solvent extraction anti SFE are not recommended as preparation techniques suitable for polar phenolics exaction from plant material. Yields of all analytes were low in comparison to liquid extraction and SPE, and the cleanness of chromatograms has also been worse than after SF with OASIS HLB sorbent.