Characterization of petroleum by high resolution field desorption/ionization and atmospheric pressure photoionization FT-ICR mass spectrometry

Two ionization methods, i.e., field desorption (FD) and atmospheric pressure photoionization (APPI), were coupled to probe the larger fraction of nonpolars (aromatic hydrocarbons, thiophenes), illustrated for the aromatic fraction of crude oil. The broadband FD-ion cyclotron resonance MS showed prominent homologous series of intact alkylated aromatics and thiophenes. Although positive-ion FD produced primarily odd-electron radical ions, APPI generated both protonated and radical cations for naphtha[a]pyrene. APPI generated five-membered pyrrolic nitrogen species as radical cations but six-membered pyridinic nitrogen species as protonated even-electron ions. Thus, five- and six-membered rings were readily distinguished by their half-integer vs. integer double bond equivalent values. This is an abstract of a paper presented at the ACS Fuel Chemistry Meeting (San Diego, CA Spring 2005).