Unprecedented Ultrahigh Resolution FT-ICR Mass Spectrometry and Parts-Per-Billion Mass Accuracy Enable Direct Characterization of Nickel and Vanadyl Porphyrins in Petroleum from Natural Seeps

The most abundant and problematic metal compounds in crude oil exist as organic complexes of vanadium and nickel in porphyrin structures derived from biological molecules (chlorophyll and heme), the first petroleum biomarkers discovered by Alfred Treibs in the early 1930s.(1) Detailed characterization of the type and structure of porphyrins is critical for development of petroleum upgrading processes, but also to link crude oil to source rock conditions. Because petroporphyrins concentrate in heavy oils, direct characterization challenges routine analytical techniques due to the increased complexity associated with heavy crudes. Atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) provides ultrahigh resolving power (m/Delta m(50%) > 1 000 000 at m/z 500) and subppm mass error (<50 ppb) to identify nickel porphyrin isotopes for unambiguous elemental composition assignment. We also report the first simultaneous identification and categorization of both vanadyl and nickel porphyrins in the same sample, without prior sample preparation. More than 85 000 mass spectral peaks are resolved and identified in a single mass spectrum, and represent the most extensive molecular deconvolution of an organic mixture characterized to date.