Chromatographic conditions
A Nova-pak C18
column (150 mm × 3.9 mm, 4 μm, Waters,
Milford, USA) was used for the chromatographic separation. The mobile phase was composed of 50 mM KH2PO4
(pH 8.5) and acetonitrile in the ratio of 50:50 (v/v) and
pumped at room temperature, at a flow rate of 1 ml/min.
The wavelength of the UV detector was set at 230 nm.
The mobile phase was degassed by filtration through a
0.45 μm filter and sonication for 5 mi