996 photodiode array (PDA) detector monitoring at
200–350 nm or a Waters 486 tunable absorbance UV
detector set at 254 nm, and an NEC computer with
MILLENNIUM (version 2.10) chromatography software.
The column used was a YMC-pack ODS-AM-303
column (5
m, 250×4.6 mm i.d.) (YMC Inc, Wilmington,
NC) equipped with an AM direct connect C-18
guard column. All HPLC analyses were performed at
ambient temperature. A Hewlett–Packard 8452A diode
array spectrophotometer was used to verify the concentrations
of stock standards prior to use.