SPEs were performed by Sep-pak C18 column (Waters,
UK). About 1mL of each sample was injected through the
SPE column and recovered by 1mL methanol (HPLC
grade, Carlo Erba Reagent, UK), and the extract was kept
in a 1mL glass vial prior to the HPLC injection. The
samples as well as standards were extracted and analysed in
triplicate.