title: Spectral characterization of ten cyclic lipids using time-of-flight secondary ion mass spectrometry.
abstract: BACKGROUND
  Over the last decade, the high lateral resolution and imaging capabilities of time-of-flight secondary ion mass spectrometry (ToF-SIMS) have increasingly stimulated interest in studying organic molecules in complex environmental materials. However, unlike with the established mass spectrometric techniques, the use of ToF-SIMS in the biogeosciences is still hampered by a lack of reference spectra of the relevant biomarker compounds. Here we present and interpret ToF-SIMS reference spectra of ten different cyclic lipids that are frequently used as biological tracers in ecological, organic geochemical and geobiological studies.
  
  
  METHODS
  Standard compounds of α,β,β-(20R,24S)-24-methylcholestane, (22E)-ergosta-5,7,22-trien-3β-ol, 17α(H),21β-(H)-30-norhopane, hope-17(21)-ene, hop-22(29)-ene, 17β(H),21β(H)-bacteriohopane-32,33,34,35-tetrol, 17β(H),21β(H)-35-aminobacteriohopane-32,33,34-triol, α-tocopherol, β,β-carotene, chlorophyll a, and cryosections of microbial mats and a fungus were analyzed using a ToF-SIMS instrument equipped with a Bi(3)(+) cluster ion source.
  
  
  RESULTS
  The spectra obtained from the standard compounds showed peaks in the molecular weight range (molecular ions, protonated and deprotonated molecules, adduct ions) and diagnostic fragment ion peaks in both, positive and negative ion modes. For the cyclic hydrocarbons, however, the positive ion mode spectra typically showed more and stronger characteristic peaks than the negative ion mode spectra. Using real world samples the capability of ToF-SIMS to detect and image selected compounds in complex organic matrices was tested. 17β(H),21β(H)-35-Aminobacteriohopane-32,33,34-triol, carotene and chlorophyll a were successfully identified in cryosections of microbial mats, and the distribution of ergosterol was mapped at µm resolution in a cryosection of a fungus (Tuber uncinatum).
  
  
  CONCLUSIONS
  This study further highlights the utility of ToF-SIMS for the identification and localization of lipids within environmental samples and as a technique for biomarker-related research in organic geochemistry and geobiology.
authors: Geobiology Group, Geoscience Centre, University of Göttingen, Goldschmidtstrasse 3, D-37077 Göttingen, Germany.
authors: Tim
authors: T
authors: Leefmann
authors: Christine
authors: C
authors: Heim
authors: Sandra
authors: S
authors: Siljeström
authors: Martin
authors: M
authors: Blumenberg
authors: Peter
authors: P
authors: Sjövall
authors: Volker
authors: V
authors: Thiel
mesh_terms: D001203:Ascomycota / Q000737:chemistry; D001419:Bacteria / Q000737:chemistry; D015415:Biomarkers / Q000032:analysis / Q000737:chemistry; D002338:Carotenoids / Q000737:chemistry; D002734:Chlorophyll / Q000737:chemistry; D000077194:Chlorophyll A; D004875:Ergosterol / Q000031:analogs & derivatives / Q000737:chemistry; D005658:Fungi / Q000737:chemistry; D008055:Lipids / Q000032:analysis* / Q000737:chemistry*; D059013:Microbial Consortia; D008970:Molecular Weight; D018629:Spectrometry, Mass, Secondary Ion / Q000379:methods*; D013729:Terpenes / Q000737:chemistry
chemical_list: D015415:Biomarkers; D008055:Lipids; D013729:Terpenes; D002734:Chlorophyll; D002338:Carotenoids; C015190:ergostane; D000077194:Chlorophyll A; D004875:Ergosterol