Separation was carried out using a Zorbax SB-C18
(2.1 mm 50 mm, 1.8 mm) analytical column (Agilent). Optimum
separation was achieved with a binary mobile phase gradient at a
flow rate of 0.4 mL/min. The column temperature was kept at 30 C
and the injection volume was 10 mL. Solvents were (A) water/acetic
acid (0.2%) pH 3.10, and (B) acetonitrile.