The linear gradient elution used was as follows: 10-15% B over 45 min; 15-
60% B over 15 min, hold for 20 min; 60 to 10% B over 1
min; column equilibration at 10% B for 20 min. The flow
rate was 0.7 mL/min, and the data were collected for 80min. The column temperature was ambient, with an
injection volume of 20 L.