The extracts were centrifugedat 7000 rpm for 6 min, and the supernatants were transferred into 100 mL round-bottom flasks. The samples were concentrated to dryness using a rotary evaporator (Büchi, Switzerland) under reduced pressure at 40оC and redissolved in 9 mL mixture of phosphate buffer (0.5 M KH2PO4, pH 3) : acetonitrile (70 : 30, v/v).Samples were cleaned up using solid phase extraction (SPE) carried on Lichrolut EN cartridges previously activated with 6 mL acetonitrile and 6 mL phosphate buffer solution (0.5 M KH2PO4, pH3). Extracts were loaded on cartridges, followed by washing with 6 mL of phosphate buffer solution and analytes were eluted with 6 mL acetonitrile. The eluates were concentrated to dryness usinga nitrogen stream at 30◦C, redissolved in 0.5 mL acetonitrile, and after filtration through 0.45 m PTFE filters were used for HPLCanalysis