Abstract:

DPPH radical scavenging properties of antioxidants are generally evaluated by determining absorbance (A517 nm) at 517 nm wavelength. Herein, the radical scavenging mechanisms of ascorbic acid on DPPH radicals were investigated by UV-Vis spectrometric, electrochemical and mass spectrometric determinations. It was found that DPPH existed in two different forms, radical form (DPPH·) and highly conjugated form (DPPH+), and ascorbic acid could scavenge both of them in the solution. Generally, the two forms of DPPH were at equilibrium in the solution. This makes it possible to indirectly evaluate DPPH radical scavenging properties of the same kinds of antioxidants based on A517 nm changes of DPPH+, but for different kinds of antioxidants, it is impossible to correctly evaluate radical scavenging properties because of their different relative scavenging effects on the two forms of DPPH.

Key words: ascorbic acid, DPPH free radical, scavenging mechanism, spectrometry, cyclic voltammetry, mass spectrometry