The origin of organic matter on the planet Mars is to be investigated through the ExoMars project using instruments including the Mars organic molecular analyzer (MOMA). The latter will analyze pristine sub-surface samples with a combination of laser desorption-ionization mass spectrometry (LDI/MS) and gas-chromatography mass spectrometry (GC-MS). In order to help interpret the data that will be produced with LDI/MS on MOMA, and for future paleontological applications, we applied high-resolution LDI/MS to fossil organic matter of a sedimentary rock from the much-studied Jurassic laminates bituminous deposit of Orbagnoux, France. Our samples host abundant sulfur-rich microbial organic matter, which are relevant for Mars exploration after thiophenes had been detected on Mars using the Sample analysis at Mars (SAM) instrument.<br/> <br/>Our ion source, a pulsed desorption laser (532 or 266 nm) shoots at a sample (that can be -cooled with liquid nitrogen), leading to a plume of neutral and ionized atoms or molecules. A second laser (266 nm) can be used to further ionize the plume expanding orthogonally. The ions are then guided to and analyzed with high-resolution (m/Δm ~ 10000 at 128 m/z) orthogonal Time-of-flight MS (by Fasmatech).<br/> <br/>We analyzed various types of subsamples, including solvent-extracted molecules (bitumen and maltene fractions), insoluble macromolecular organic matter demineralized with HF and HCl (kerogen), rock powder, and polished rock slice. Carbon clusters and their hydrogenated and S-rich counterparts were detected in all fractions. Polyaromatic hydrocarbons were detected in all fractions, but the slice. The intense signal obtained on the extracts allowed the detection of additional oxygenated molecules and alkylbenzenes. An increasing contribution of inorganic species was seen from kerogen&lt;fresh rock&lt;slice. Analysis of Orbagnoux samples thus shows that LDI/MS can have access to both soluble and insoluble organic fractions, and those diverse molecules can be distinguished in mineralized samples.

Characterization of sedimentary organic matter using laser desorption-ionization mass spectrometry

ACS Spring Meeting 2021

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