Resolution of 11,000 compositionally distinct components in a single electrospray ionization Fourier transform ion cyclotron resonance mass spectrum of crude oil.

Mass spectrometry is well-suited for complex mixture analysis, because unlike other types of spectroscopy, the number of mass spectral peaks per analyte is of order one. Here, we extend significantly the upper limit for the number of chemically distinct components resolved and identified in a single step. Specifically, electrospray selectively ionizes only the basic compounds (i.e., a small fraction of the entire chemical composition) in a sample of South American crude oil. Nevertheless, their positive ion Fourier transform ion cyclotron resonance mass spectrum (average mass resolving power of approximately 350,000 from 225 to 1000 Da) contains more than 11,100 resolved peaks, of which >75% may be assigned to a unique elemental composition (CcHhOoNnS8). Mass scale expansion and graphical representations reveal increased heteroatom diversity, aromatic rings, and alkyl substitution with increased mass. These results set a new standard and illustrate the potential of high-resolution mass spectrometry for analysis of compositionally complex chemical mixtures.