Experimental
1. Equipments
A Shimadzu LC-10AD HPLC integrated with a Class-LC10 system was used with an UV-visible detector. For data acquisition, a Shimadzu SPD-10A softwarewas used. Separations were achieved using a 250mm×4.6mmPhenomenex LiChrospher® 100–RP18 5_m C18 column.
Samples and standard solutions were chromatographed at ambient temperature (24.0±2.0 ◦C), using 0.2% metaphosphoric acid/methanol/acetonitrile (90:8:2, v/v/v) as the mobile phase (flow rate of 1.0mLmin−1) with detection at 254 nm and injection volume of 20 _L.