Investigation of MALDI-TOF mass spectrometry of diverse synthetic metalloporphyrins, phthalocyanines and multiporphyrin arrays

We investigated the utility of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) for analyzing porphyrinic c ompounds using a variety of different synthetic porphyrins, azaporphyrins, phthalocyanines and multiporphyrin arrays. Comparisons of spectra obtained from these analytes deposited either as near samples or codeposited with ne utral or acidic matrices have been made with the goal of identifying condit ions that yield minimal demetalation, transmetalation, adduct formation and fragmentation, It was found that the molecular masses of many porphyrins c an be successfully measured from neat sample preparations and do not requir e a matrix to facilitate desorption and ionization, although the measuremen t of large multiporphyrin arrays was facilitated by the use of matrices. De metalation of magnesium porphyrins occurred in the presence of acidic matri ces, but not with neutral matrices such as 1,4-benzoquinone. Positive ion s pectra were obtained for each compound acid negative ion spectra were also collected for the azaporphyrins and phthalocyanines. Examination of selecte d samples (prepared neat, with 1,4-benzoquinone, 2,3,5,6-tetrachloro-1,4-be nzoquinone or alpha-cyano-4-hydroxycinnamic acid) showed that the dominant process of ionization involved oxidation yielding the radical cation M+ rat her than the protonated molecule [M+H](+) MALDI-TOF-MS is shown to be a pow erful analytical tool for the characterization of diverse synthetic porphyr inic compounds. Copyright (C) 1999 John Wiley & Sons, Ltd.