Two possible reasons for these phenomena are proposed.
First, as discussed in Section 2.1, Aconitines could be
hydrolyzed to form Benzoylaconines at high temperature.
This hydrolysis was also promoted when the pH increased,
and it was observed by Yue et al. (2008) that the concentrations
of Aconitines were markedly decreased and the concentration
of Benzoylaconines became much higher as pH
increased. This indicated that this hydrolysis could be
classified as alkaline hydrolysis (Singhuber et al., 2009; Ohta
et al., 1997; Yue et al., 2008). Thus the stability of Aconitines
was weak in alkaline solution and they were more easily
degraded. The second possible reason was related to ozone.
Ozone was generated by plasma when oxygen was present in
the reactor. In addition to the direct reaction of Aconitum
alkaloids and ozone, when the reaction took place in alkaline
solution the OH− species could enhance the decomposition of
O3 and produce hydroxyl radical. The oxidizing ability of the
hydroxyl radical is much higher than that of ozone. As a
result, more Aconitum alkaloids were degraded because of the
increase in hydroxyl radical. These two pathways both
contribute to the degradation of Aconitum alkaloids. Thus the
degradation ratios of Aconitum alkaloids rise in alkaline
solution. Though some of the hydroxyl radicals probably
would combine with OH− to form water and decrease the
concentration of hydroxyl radical at high levels of hydroxyl
radical, the influence is very small.