Exact masses (±0.0001 u) are tabulated (Cmin− C50) for free-base, Mn, Fe, Ni, Cu, Zn, vanadyl (VO), and Ga complexes of the major geoporphyrin skeletal types and several commercially available porphyrin complexes. The data in these tables are intended as a resource to aid in geoporphyrin identification (i.e. determination of carbon number, skeletal type and metal chelated) by low-resolution electron ionization-mass spectrometry (EI-MS) and by high-resolution EI-MS in cases where exact mass determination is performed. A comparison is made of the isotope patterns calculated for the molecular ions of the various porphyrin skeletal types as free-base species and as the seven metal complexes mentioned above. The isotope pattern of a metalloporphyrin molecular ion is shown to be a useful aid in identifying the metal complexed. Correction of molecular ion abundances (i.e. porphyrin abundances) for overlap of molecular ion isotope peaks and for overlap of fragment ion peaks with molecular ion peaks, both of which can occur when analyzing complex geoporphyrin mixtures, is discussed.

Fast Atom Bombardment-Mass Spectrometry (FAB-MS) and Electron Ionization-Mass Spectrometry (EI-MS) at 12 and 70 eV, were used to obtain mass spectra of mesoporphyrin IX dimethylester (DME), tetraphenylporphyrin (TPP), octaethylporphyrin (OEP), and the metalloporphyrins, Ni(DME), Ni(TPP), Ni(OEP), VO(TPP), VO(OEP), as well as a VO(II) porphyrin concentrate obtained from the New Albany oil shale bitumen (Mississippian-Devonian). A mixture of dithiothreitol/dithioerythritol (“Magic Bullet”) was used as the FAB matrix. Greater fragmentation of free-base and metalloporphyrins was observed in FAB mass spectra compared to the EI mass spectra. Adduct ions formed by addition of sulfur and a matrix molecule to the porphyrins were observed. In FAB spectra of the VO(II) complexes, loss of oxygen was noted. The FAB mass spectra of mixtures of VO(II) geoporphyrins are much more complex than corresponding EI mass spectra because of the greater fragmentation and the multiplicity of ions (M+, M + H, M + 2H, etc.) observed in the FAB mode. Using the matrices investigated, FAB is less suitable for EI for the mass spectrometric analysis of the geoporphyrins.