C18-columns were used both on UHPLC and on HPLC. The HPLC
method was used for many years in the lab. Now, we tried some
new conditions with different column temperature and solvent
flow rate, and found that 40 C was better suited than 20 C.
Comparing with the HPLC method at 20 C, the better resolution
at 40 C on UHPLC resulted in sharp peaks in the UHPLC chromatogram
for the FOG compounds. Furthermore, rutin and K-grg
were separated on UHPLC under the selected condition, while
there was no separation on HPLC. The contents of these two compounds
were really different in different teas, and green tea samples
contained more K-grg while oolong tea and black tea had
much more rutin. The separation of these two compounds was further
confirmed with the addition of rutin solution to both green tea
and oolong tea samples. It is not clear whether or not this different
content is due to clone, geographic origin or manufacture or to a
combination of all factors.