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Communication Dans Un Congrès Année : 2018

Resolution of Fatty Acids in Mars-Analog Samples with the SAM Instrument TMAH Wet Chemistry Experiment

Résumé

The Curiosity rover is exploring sedimentary rock sequences in Gale Crater for evidence of habitability and searching for organic compounds using the Sample Analysis at Mars (SAM) instrument suite. SAM includes a gas chromatograph mass spectrometer (GC-MS) and pyrolysis ovens. SAM has the capability to perform wet chemistry experiments, one of which uses tetramethylammonium hydroxide (TMAH) thermochemolysis to liberate free and bound carboxylic acids including fatty acids making them sufficiently volatile for detection by GC-MS. To determine the effectiveness of the TMAH experiment on fatty acid methyl esters (FAMEs) from terrestrial organisms, a variety of Mars-analog sedimentary samples were analyzed, including: 1) iron oxides from a modern mineral precipitate and older surface gossan at Iron Mountain, CA; 2) mixed iron oxides and clays from modern acid and neutral salt lakes in Western Australia; 3) siliceous sinter from modern Icelandic hot spring deposits; 4) modern carbonate ooids from shallow sand shoals in the Bahamas; and 5) organic-rich shale from the Eocene Messel oil shale in Germany. Fatty acids from the samples were pyrolyzed with TMAH using a SAM-like pyrolysis heating ramp (35°C/min) or a 500°C flash pyrolysis on a commercial Frontier pyrolyzer and Agilent GC-MS instrument. Thirty seven FAMEs in a standardized mixture were analyzed on the SAM flight spare GC columns to determine the largest FAME that may pass through the columns under SAM conditions. The largest FAME that would pass through SAM's GC4 column is C12:0. Additionally, FAMEs in Mars-analog samples analyzed on a commercial instrument were detected with the TMAH experiment. C6:0-C10:0 FAMEs were present in all samples, C11:0-C18:2 FAMEs were present in select samples, and C20:0-C30:0 FAMEs were present in the shale sample. This demonstrates that TMAH thermochemolysis with SAM-like pyro-GC-MS on a commercial instrument is effective in FAME generation and detection from Mars-analog samples that vary in mineralogy, age, and microbial community input, and that FAMEs up to C12:0 could be detected with the SAM instrument. Iron oxides mixed with clays are known to be present on Mars in the path of the Curiosity rover, and our results indicate that this environment may provide the optimal opportunity to detect fatty acids, if present, in Gale Crater.
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Dates et versions

insu-04426200 , version 1 (30-01-2024)

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A. J. Williams, J. L. Eigenbrode, R. Williams, Maëva Millan, S. S. Johnson, et al.. Resolution of Fatty Acids in Mars-Analog Samples with the SAM Instrument TMAH Wet Chemistry Experiment. American Geophysical Union, Fall Meeting 2018, Dec 2018, Washington, United States. ⟨insu-04426200⟩
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