Rationale: Diphenylamine (DPAH) and its derivatives have been widely used as antioxidants. Its antioxidation behaviors are started with the formation of diphenylamino radical (DPA ) by loss of hydrogen atom through reaction with oxygen or ozone. DPAH was oxidized by ozonation to produce DPA and DPA was directly detected using atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The influence of oxidation time on generation of DPA and consumption of DPAH was also investigated.
Methods: Experiments were performed using a home-made ozone bubbling apparatus for oxidation of DPAH. DPAH solution (1000 ppm) in acetone was stirred during the ozonation. The oxidized sample was diluted 100-fold and analyzed using APCI-MS. Structures and energies of DPAH, DPA and detected ions were obtained using electronic structure calculations with Spartan 10 and Gaussian 09.
Results: DPA was detected in positive APCI-MS in the form of DPAH by proton transfer reaction with protonated acetone. Formation of DPAH from DPA was more favorable than that of [DPAH + H] from DPAH and it was also much more favorable than that of DPA from DPA . By increasing the oxidation time, the relative abundance of DPAH was increased whereas that of [DPAH + H] was notably decreased.
Conclusions: Existence of DPA was directly analyzed using APCI-MS. DPAH and DPA were differently detected as [DPAH + H] and DPAH , respectively. Direct APCI-MS analysis is a suitable technique for identification and quantitation of DPA .
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