The flow rate was maintained at 1 mL/min for the mobile phase, and was con-trolled by binary pumps at 40 ◦C. The mobile phase was a linear gradient of acetonitrile with 0.1% formic acid (A) and water with 0.1% formic acid (B). The gradient extended from 0 to 20 min and consisted of 40–100% A. The resultant effluent was monitored at 280 nm; the UV spectrum range of the effluent was 200–400 nm.