THE LC/MS/MS CHARACTERIZATION OF PHOTOLYSIS PRODUCTS OF BENZOTRIAZOLE-BASED ULTRAVIOLET ABSORBERS

The photodegradation of Tinuvins P, 328, and 900 (Ciba-Geigy) under mild conditions was confirmed by conducting photolysis in methanol, ethanol, and acetonitrile solvents with azo(bis)isobutyronitrile (AIBN, a radical source) or cumene hydroperoxide. Benzotriazole was the major photolytic product observed. In addition to cleavage products, adducts of the parent UV absorber (WA) were also observed. The identities of various photoproducts were determined by HPLC with UV diode array detection and by combined HPLC and tandem mass spectrometry (MS/MS). Among the photoproducts identified by MS/MS were benzotriazole, phenolic fragments, and solvent-UVA adducts. The photoproducts identified provide evidence that photochemical degradation is initiated by chemical attack on the phenol ring, which can result in cleavage of the benzotriazole functionality, displacement addition of radicals to the phenolic ring, loss of alkyl ligands from the phenolic ring, and loss of unsaturation in the phenolic ring. The predominance of mass spectral evidence did not support a reaction pathway involving the phenyl hydroxyl group.