We have coupled atmospheric pressure photoionization (APPI) to a home-built 9.4-T Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Analysis of naphtho[2,3-a]pyrene and crude oil mass spectra reveals that protonated molecules, deprotonated molecules, and radical molecular ions are formed simultaneously in the ion source, thereby complicating the spectra (>12 000 peaks per mass spectrum and up to 63 peaks of the same nominal mass), and eliminating the "nitrogen rule" for nominal mass determination of number of nitrogens. Nevertheless, the ultrahigh mass resolving power and mass accuracy of FT-ICR MS enable definitive elemental composition assignments, even for doublets as closely spaced as 1.1 mDa (SH3(13)C vs (12)C4). APPI efficiently ionizes nonpolar compounds that are unobservable by electrospray and allows nonpolar sulfur speciation of petrochemical mixtures.

Vanadyl porphyrins are detected and characterized by their double-bond equivalents (DBE = number of rings plus double bonds) and carbon number in an unfractionated (raw) asphaltene and unaltered South American crude oil. Atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) provides the high mass-resolving power (450 000−650 000 at m/z 500) and accurate mass (<300 ppb) to unambiguously assign elemental compositions to each of more than 10 000 peaks in each mass spectrum. Kendrick mass sorting revealed unusually high mass errors for peaks assigned to high DBE O2 species as well as a suspicious bimodal distribution in plots of DBE versus carbon number for all O2 species. Inclusion of vanadium in the chemical formula assignment resolved the bimodal distribution into lower DBE O2 species and vanadyl porphyrins, with a subsequent decrease in mass assignment errors to the same level as those for the thousands of other identified species. Vanadyl porphyrins are detected as both M+  • and [M + H]+ molecular and quasimolecular ions. Trends in the relative abundance of specific DBE values reveal the structural diversity of the vanadyl porphyrins in the asphaltene and heavy crude oil. To our knowledge, the current results are the first to directly identify and catalog the structural diversity of vanadyl porphyrins directly in raw (unfractionated) asphaltene and unaltered heavy crude oil.

Fourier‐transform ion cyclotron resonance mass spectrometry (MS) has demonstrated potential to revolutionize the fields of limnology and chemical oceanography by identifying the individual molecular components of organic matter in natural waters. The use of MS for this purpose is made possible by the electrospray technique which successfully ionizes polar, nonvolatile organic molecules. Another recently developed ion source, atmospheric pressure photoionization (APPI), extends MS capabilities to less polar molecules. This article presents early results on the application of APPI MS to natural organic matter. We compare APPI MS and electrospray MS data for dissolved organic matter from Lake Drummond (Virginia, USA). Collectively, electrospray and APPI MS identify more than 6000 molecular species to which we assign unique molecular formulas. Fewer than 1000 molecular species are common to both electrospray and APPI mass spectra, indicating that the techniques are highly complementary in the types of molecules they ionize. Access to a broad range of molecules provided by combining APPI and electrospray has prompted a qualitative analysis. The goal is to assess the extent to which molecular MS data correspond with elemental (CHNOS) and structural characteristics determined by combustion elemental analyses and 13C nuclear magnetic resonance (NMR). Because the data obtained by these different methods are not directly comparable, we propose a novel data analysis procedure that facilitates their comparison. The bulk elemental composition calculated from electrospray MS data are in close agreement (± 15%) with values determined by combustion elemental analysis. APPI and electrospray MS detect protein contributions in agreement with 13C NMR (6 wt %) but underestimate carbohydrates relative to 13C NMR. Nevertheless, MS results agree with NMR on the relative proportions of noncarbohydrate compounds in the organic matter: lignins > lipids > peptides. Finally, we use a molecular mixing model to simulate a 13C NMR spectrum from the MS datasets. The correspondence of the simulated and measured 13C NMR signals (74%) suggests that, collectively, the molecular species identified by APPI and electrospray MS comprise a large portion of the organic matter in Lake Drummond. These results add credibility to electrospray and APPI MS in limnology and oceanography applications, but further characterization of ion source behavior is fundamental to the accurate interpretation of MS data.