An Agilent 1260 Infinity HPLC system (Agilent Corporation, USA) equipped with a vacuum degasser, an auto-sampler, a quaternary pump, an analytical guard column (Eclipse XDB-C18, 5 mm particle size, 12.5 mm 4.6 mm i.d.; Agilent Corporation, USA), and a G1315D diode-array detector (DAD) was used for chromatographic analysis