Identification of photochemical oxidation products of 5,10,15,20-tetra(m-hydroxyphenyl)chlorin by on-line high-performance liquid chromatography-electrospray ionization tandem mass spectrometry

An on-line HPLC-electrospray ionization tandem mass spectrometry system has been developed for the separation and characterization of the photochemical oxidation products of 5,10,15,20-tetra (m-hydroxyphenyl)chlorin (m-THPC), a new photodynamic therapeutic agent. m-THPC was photo-oxidized in methanol solution by exposure to white laboratory light for one week. The products were then separated by isocratic elution on an Apex C-18 column with 0.1% trifluoroacetic acid in acetonitrile (23:77, v/v) as mobile phase and characterized on-line by electrospray tandem mass spectrometry. The results showed the formation of 5,10,15,20-tetra(m-hydroxyphenyl) porphyrin (m-THPP), hydroxy m-THPP and three hydroxy m-THPC isomers. Hydroxylation on the reduced pyrrole ring of m-THPC was the most prominent reaction.