Characterising the Influence of Phyllosilicate Clay Minerals on Fatty Acids During Py-GC/MS Analysis

The search for organic matter on Mars has yielded the detection of C₂-C₄ dichloroalkanes and chlorobenzene, as well as other aromatic, thiophenic and aliphatic compounds. The role of minerals or the associated mineral matrix in this search is important. Minerals can preserve and protect organic matter from environmental stressors, but they can also prevent detection through their reactions with organic matter during (thermal) analysis. Proposed Mars-relevant examples of such analytical artefacts include the roles of perchlorate and sulphate minerals. Thermal analysis such as, pyrolysis-gas chromatography-mass spectrometry (py-GC/MS) uses high temperatures to fragment and/or release macromolecular organic matter from sampled material. This technique is utilised by both the Sample Analysis at Mars (SAM) and the upcoming ExoMars, Mars Organic Molecule Analyser (MOMA) instruments.

Clays are good preservers of organic matter and are the defining mineralogy of the ExoMars landing site options. Terrestrial studies demonstrate the occurrence of clay-induced analytical artefacts during py-GC/MS - interactions which are less understood in the Mars context but are potentially critical for mission success. To begin to address this, this study combines several single-phase phyllosilicate minerals with fatty acids: stearic and oleic acid. Fatty acids are well-preserved in the terrestrial geological record and are potential biosignature targets for Mars missions. The resulting products of fatty acid pyrolysis in the presence of these clay minerals and the major fragment changes induced will be presented, and the reaction mechanisms discussed.