The analysis
was performed by the HPLC system equipped with a DAD at
215 nm with a Luna RP-C18 column (250 4.6 mm, 5 mm, Phenomenex,
Torrance, CA, USA).
Milli-Q water acidified with H2SO4
12M(pH 2.55) was used as mobile phase on isocratic gradient with
a flow rate of 0.4 ml/min