Ion trap tandem mass spectrometry study of dexamethasone transformation products on light activated TiO2 surface

The photocatalytic transformation of dexamethasone and the formation of its intermediate compounds have been studied using titanium dioxide as a photo catalyst. The degradation of dexamethasone occurs easily through the format ion of several hydroxy derivatives whose characterization has been made by HPLC/MS/MS. Even if both oxidative and reductive processes can be operating , only oxidative products have been identified in air saturated aqueous sus pensions. A pattern of reaction pathways accounting for the observed interm ediates is proposed. The obtained experimental evidence may be rationalized postulating the existence of a double initial mechanism. A single oxidatio n step resulting from the attack by one (OH)-O-. radical leading to the for mation of five hydroxy-derivatives and a concomitant attack involving two ( OH)-O-. radicals leading to the hydroxylation of the quinoid moiety of the molecule. (C) 2001 American Society for Mass Spectrometry.