equipped with a VertiSep column (4.6mm×150mm, 5m, Vertical Chromatography, Thailand) and a gradient elution using 0.4% formic acid in water–methanol from 100:0 (v/v) at 0min up to 95:5 (v/v) at 2min, 70:30 (v/v) at 5min, 66:34 (v/v) at 8min, 45:55 (v/v) at 11–14 min, then up to 0:100 (v/v) after 17 min. Flow rate was 1.0 mL/min and the column temperature of 30 ◦C