Here we introduce the analysis of the 1,1-diphenyl-2-picrylhydrazyl free radical (DPPH radical), which is known as a stable radical. When analyzed using reversed-phase HPLC, a peak should be 1,1-diphenyl-2-picrylhydrazine (DPPH) was detected as a DPPH radical impurity. For this reason, we checked the retention time and the UV-VIS spectrum obtained with a diode array detector. Acetonitrile dehydrated with molecular sieves was used for sample dilution.
From the calibration curve and the chromatogram at low concentration, a certain amount was decomposed before injection, and it was confirmed that it changed even in the HPLC system.