Characterization of petroleum products by laser-induced acoustic desorption in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer .

摘要

Many petroleum products, in particular large nonpolar saturated hydrocarbons, have proven difficult to analyze via mass spectrometry due to their low volatility, lack of basic or acidic groups needed for most ionization methods, and low activation energies for fragmentation after ionization.;The above limitation has been addressed by using laser-induced acoustic desorption (LIAD) to evaporate nonvolatile and thermally labile petroleum components for analysis in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The gaseous neutral analytes were ionized by electron impact. Model compounds were studied first to test the viability of this method. After that, different types of asphaltenes were characterized successfully. For example, the molecular weight distribution of a North American asphaltene was determined. A comparison between asphaltene samples obtained from different geographical locations showed distinct molecular weight characteristics, possibly allowing for the determination of an unknown asphaltene sample's geographic origin.;Asphaltenes were also characterized via electrospray ionization (ESI) in a linear quadrupole ion trap (LQIT). The observed molecular weight distribution had an extended tail past 2000 Da. Collision-activated dissociation (CAD) experiments on isolated ions revealed that water aggregation was present in this analysis. The observed molecular weight distribution of asphaltenes reduced dramatically when water was eliminated from the system.;The usefulness of a new chemical ionization reagent, ClMn(H2O) +, is also discussed. This reagent has been shown to ionize hydrocarbons without fragmentation to yield [ClMnR]+, where R is the hydrocarbon, thus providing molecular weight information. CAD of the [ClMnR]+ ions is demonstrated to allow the differentiation of isomeric hydrocarbons. Finally, the LIAD/ClMn(H2O)+ mass spectrometric method was applied to the successful analysis of various petroleum fractions and asphaltene-like compounds.