Fundamentals of Molecular Formula Assignment to Ultrahigh Resolution Mass Data of Natural Organic Matter

Ultrahigh-resolution mass spectrometry via the Fourier
transform ion cyclotron resonance technique (FT-ICR-MS)
allows the identification of thousands of different molecular formulas in natural organic matter and petroleum
samples. Molecular formula assignment from mass data
is most critical and time-consuming for these samples,
and in many cases, several formulas can be determined
for the same molecular mass. Therefore, automated
procedures are required for an efficient exploitation of the
extensive data sets. Here, we revise statements in a recent
publication, which might result in a misleading impression about our approach of formula assignment in a
previous work. We also summarize and categorize existing
procedures for formula assignment. In addition, we
propose new techniques, which are suitable to be implemented in automated evaluation software. The homologous series approach is extended toward a building block
approach that can be applied as a new exclusion criterion
for incorrect formula assignments. The examination of
stable isotope ratios of individual molecules in natural
organic matter can be applied as an additional and
intrinsic evaluation for calculated molecular formulas.