2.2. HPLC apparatus and conditions
The analysis was performed on a Shimadzu SPD-10A (Japan)
HPLC equipped with a quaternary solvent delivery system with
model LC-10AD pump, a DGU-10A degasser, UV–vis detector SPD-
10AV and auto-injector SIL-10AD. The separation was carried out
on a Hypersil BDS C-18 column (4.6 mm
×
150 mm i.d., 5 m) with a
C-18 guard column. The elution was performed on isocratic solvent
system using methanol: 1 mM ammonium acetate solution (55:45)
at a flow rate of 1.0 ml/min. The detection was monitored at 295 nm
while injection volume for all the samples and standards was 10 L.
Prior to injection, all solutions were filtered through a 0.2 m nylon
membrane filter. The HPLC method was validated according to our
previous report (Kongkiatpaiboon and Gritsanpan, in press). Each
sample was analyzed in triplicate