The performance of the system stability was evaluated over
three different time intervals (2, 7 and 12 h after it was initially
set up and tested. We found that our on-line HPLC-FRSD system
was very stable within 7 h. The RSD values (%) represented the stability
of the HPLC-FRSD system varied from 0.78% to 15.73% in online
HPLC-ABST-FRSD assay, and from 0.68% to 7.49% in the on-line
HPLC-DPPH-FRSD assay. In a previous on-line HPLC-DPPH method,
the authors reported the system was stable within 12 h (Zhang
et al., 2013). For our new on-line HPLC-FRSD system, we suggested
that the free radical solutions be replaced after 7 h considering the
stability of the free radicals (Arnao, 2000). However, the reason for
the difference of stability could be caused by the difference of kinds
of analytes or samples.