2.11. On-line HPLC–DPPH assay
The extracts were analysed on a HPLC/UV system supplemented
with DPPH
radical scavenging detector. In this system two chromatograms were recorded simultaneously, one of which representing UV absorbance of effluent at 265 nm prior to the reaction,
while a mirror chromatogram was obtained recording absorbance
at 517 nm after reaction of effluent with DPPH
solution in the
reaction coil. The mobile phase was supplied to the column by a
model 9012 HPLC gradient pump (Varian. USA) at flow rate
0.75 ml/min. The samples of 20ll were injected into the HPLC system by means of Cheminert C1 injector (Valco Instruments, USA).
Reverse-phase LiChroSpher RP-18e 5lm 12.50.4 cm column
and 0.50.4 cm precolumn (Merck, Germany) were used for separation. The DPPH
reagent was prepared by dissolving 0.01 M
DPPH
in 0.1 M sodium citrate buffer (pH 7.6), methanol and acetonitrile (50:25:25 v/v). It was continuously supplied into a reaction
coil (3 m of 0.25 mm id fused-silica capillary) by a model 2200
HPLC pump (Bischoff, Germany) at a flow rate of 0.75 ml/min. Signals were acquired at 265 and 517 nm wavelengths by means of
Linear 206 PHD and Linear UVIS 200 UV–VIS detectors, respectively. Solution A (bidistilled water with 0.05% TFA) and B (methanol with 0.05% TFA) were used as the mobile phase components for
gradient elution. Extracts were separated using the following gradient: 10% of B at 0 min, 25% of B at 5 min, 40% of B at 25 min.
95% of B at 40 min. 95% of B at 43 min and 10% of B at 44 min. Clarity chromatography software (DataApex. Czech Republic) was used
for data acquisition.