oa Investigating the Intramolecular Isotopic Structure of Isoprenoids Using Orbitrap Mass Spectrometry

Isoprenoids are a class of ubiquitous organic compounds constructed from C5 isoprene units. Pathways for their biosynthesis are highly conserved and distinct among the Domains of Life. Since the intramolecular isotopic composition of molecules strongly depends on the pathways by which they are synthesized, as well as the degree of conversion of their intermediates and the sources of their substrates, characterization of intramolecular isotopic signatures may allow for the recapitulation of these processes. Chemical and NMR methods for the study of intramolecular isotopic signatures, however, require large quantities of analyte (∼mmol), which is generally not feasible for geological samples. Here, we investigate the intramolecular carbon isotopic structure of phytane from chlorophyll of the cyanobacterium Anacystis nidulans (MEP phytane) and archaeol from the archaeon Halobacterium sp. NRC-1 (MVA phytane) at natural abundance (∼10 nmol). Orbitrap measurements were standardized relative to a commercially available phytane of unknown petrogenic origin and compared for bulk compound specific isotopic values via GC-irMS. Although intramolecular isotopic differences between analytes were not significant for mass fragment 85 m/z, our results demonstrate for the first time the accurate and precise detection of intramolecular isotopologues of large biomarker compounds at natural abundances using Orbitrap mass spectrometry.