4.4 Article

Influence of Calcium Perchlorate on the Search for Organics on Mars with Tetramethylammonium Hydroxide Thermochemolysis

Journal

ASTROBIOLOGY
Volume 21, Issue 3, Pages 279-297

Publisher

MARY ANN LIEBERT, INC
DOI: 10.1089/ast.2020.2252

Keywords

Calcium perchlorate; TMAH thermochemolysis; Pyrolysis-GC-MS; Mars; SAM and MOMA

Funding

  1. French Space Agency (Centre National d'Etudes Spatiales)
  2. SAM/MOMA funding
  3. CSC scholarship [201701810036]
  4. Universidad Nacional Autonoma de Mexico [PAPIIT IN111619]

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This study investigated the products and decomposition mechanism of TMAH pyrolysis on Mars in the presence and absence of calcium perchlorate at different heating rates. Additionally, the impact of calcium perchlorate on the recovery rate of fatty acids with TMAH thermochemolysis was studied. Results show that calcium perchlorate has no significant effect on TMAH degradation and recovery rate of fatty acids, which is promising for future organic matter detection missions on Mars.
The Mars Organic Molecule Analyzer (MOMA) and Sample Analysis at Mars (SAM) instruments onboard the Exomars 2022 and Mars Science Laboratory rovers, respectively, are capable of organic matter detection and differentiating potentially biogenic from abiotic organics in martian samples. To identify organics, both these instruments utilize pyrolysis-gas chromatography coupled to mass spectrometry, and the thermochemolysis agent tetramethylammonium hydroxide (TMAH) is also used to increase organic volatility. However, the reactivity and efficiency of TMAH thermochemolysis are affected by the presence of calcium perchlorate on the martian surface. In this study, we determined the products of TMAH pyrolysis in the presence and absence of calcium perchlorate at different heating rates (flash pyrolysis and SAM-like ramp pyrolysis with a 35 degrees C center dot min(-1) heating rate). The decomposition mechanism of TMAH pyrolysis in the presence of calcium perchlorate was studied by using stepped pyrolysis. Moreover, the effect of calcium perchlorate (at Mars-relevant concentrations) on the recovery rate of fatty acids with TMAH thermochemolysis was studied. Results demonstrate that flash pyrolysis yields more diversity and greater abundances of TMAH thermochemolysis products than does the SAM-like ramp pyrolysis method. There is no obvious effect of calcium perchlorate on TMAH degradation when the [ClO4-] is lower than 10 weight percent (wt %). Most importantly, the presence of calcium perchlorate does not significantly impact the recovery rate of fatty acids with TMAH thermochemolysis under laboratory conditions, which is promising for the detection of fatty acids via TMAH thermochemolysis with the SAM and MOMA instruments on Mars.

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