To our knowledge, because anthraquinone glycosides in
Dahuang, active ingredients with purgative functions, are
instable to heat and prone to transfer into anthraquinones [7],
the decocting time of Dahuang should be shorter than that of
other drugs. Therefore, a preliminary experiment was carried
out to find the best time point for Dahuang to be added. The
following time points were observed: to be decocted for the
same time as other drugs (0 min), to be added 3, 5, and 10 min,
respectively, before the end of decocting period or only be
dissolved in decoction of other drugs for 5 min without
cooking. Then the ingredients in the above samples were
determined and evaluated. The obtained optimal time point
was applied in future experiments.