Organic Geochemical Microanalysis by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS)

Time-of-flight secondary ion mass spectrometry(ToF-SIMS) is a powerful method for the chemicalanalysis of solid surfaces. In this paper, thecapabilities and limitations of this technique andthe potential for its use in geochemical research areoutlined. Using ToF-SIMS, the chemical compositionof sample structures down to 10–100 μm can bedetermined, without the need for pre-selection orlabelling of the analysed substances. In addition,the lateral distribution of organic and inorganiccompounds can be mapped in geochemicalsamples at a resolution in the micrometre range.The capabilities of the technique in geochemistryare illustrated by two examples. In the first example,it is shown that ToF-SIMS can be used to detectbiomarkers in oil samples, making it a promisingmethod for the analysis of biomarkers in fluidinclusions. In the second example, a number ofspecific lipid biomarkers were identified andmapped on the surface of a microbial matcryosection surface. Post-measurement opticalmicroscopy correlated the localisation of the lipidswith the presence of methanotrophic archaea in themicrobial mat.