Tabulation of exact masses and comparison of isotope patterns expected for geoporphyrin molecular ions in electron ionization mass spectra

Abstract

Exact masses (±0.0001 u) are tabulated ( C min− C 50) 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.