2.2. Chromatographic conditions
The HPLC system was Waters 2695 Alliance systems controlled
with Waters Empower 2 software. We followed the
same chromatographic conditions described previously.2 We
used a Phenomenex (Torrance, CA, USA) Prodigy ODS-3,
3 lm, 4.6 · 150 mm column. The column temperature was
set at 50 C. The autosampler temperature was kept at 4 C.
Eluent components were 0.1% H3PO4 and acetonitrile. The
proportion of acetonitrile was varied from 15% to 40% in
7.5 min, back to 15% in 0.1 min, and held at 15% for
2.4 min. The flow rate was 1.0 mL/min. The detection wavelength
was 280 nm. The injection volume was 10 lL.