Mass Resolving Power Requirement for Molecular Formula Determination of Fossil Oils

Ultrahigh-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been demonstrated to be capable of resolving doublets with mass difference of an electron. However, this resolving power can still be insufficient for positively identifying all of the overlapping species in petroleum and other fossil oils. To look into the ultimate resolving power required, we investigated all possible overlaps in molecular masses of monoisotopic, ¹³C- and ³⁴S-containing hydrocarbon and heterocompound species that are commonly found in petroleum. Among homologous series containing up to 3 heteroatoms and with up to 30 double bond equivalences, it was found that over 80% even-mass and 50% odd-mass series have overlapping series with mass differences less than an electron mass of 0.458 mDa (458 μDa). Previously introduced nominal mass series are recommended to use as additional means of differentiating the overlapping series. However, the ultimate resolving power required for resolving all possible overlaps is 0.1 mDa, less than the mass of an electron. This should be one of the goals for developing future mass spectrometers with higher resolving power