Laser-induced acoustic desorption/Fourier transform ion cyclotron resonance mass spectrometry for petroleum distillate analysis

Laser-induced acoustic desorption (LIAD) coupled with a 3-T Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR) allows the simultaneous analysis of both the nonpolar and polar components in petroleum distillates. The LLAD/Fr-ICR method was validated by examining model compounds representative of the various classes of polar and nonpolar hydrocarbons commonly found in petroleum. LIAD successfully desorbs all the compounds as intact neutral molecules into the FT-ICR. Electron ionization (El) at low energies (10 eV) and chemical ionization using cyclopentadienyl cobalt radical cation (CpCo.+) were employed to ionize the desorbed molecules. The El experiments lead to extensive fragmentation of many of the hydrocarbon compounds studied. However, the CpCo.+ ion ionizes all the hydrocarbon compounds by producing only pseudomolecular ions without other fragmentation, with the exception of one compound ((CH3)-C-. loss occurs). Examination of two different petroleum distillate samples revealed hundreds of compounds. The most abundant components have an even molecular weight; i.e., they are likely to contain no (or possibly an even number of) nitrogen atoms.