Impact of Calcium perchlorate on the TMAH thermochemolysis reaction: application to SAM and MOMA
Yuanyuan He  1, *@  , Arnaud Buch  2@  , Cyril Szopa  3, 4@  , Caroline Freissinet  5@  , Fabien Stalport  6@  , Francois Raulin  6@  
1 : Laboratoire de Génie des Procédés et Matériaux - EA 4038
CentraleSupélec
CentraleSupélec - Bâtiment Eiffel - 3 rue Joliot Curie 91190 GIF-SUR-YVETTE -  France
2 : Laboratoire de Génie de Procédés et Matériaux  (LGPM)
Ecole Centrale Paris
Grande voie des vignes, 92295 Chatenay-Malabry -  France
3 : Institut Universitaire de France  (IUF)
Institut universitaire de France, Institut universitaire de France
4 : Laboratoire Atmosphères, Milieux, Observations Spatiales
Université de Versailles Saint-Quentin-en-Yvelines : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Sorbonne Université : UMR8190, Centre National de la Recherche Scientifique : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190, Institut national des sciences de l\'Univers : UMR8190
11 boulevard dÁlembertQuartier des Garennes 78280 - Guyancourt -  France
5 : Laboratoire Atmosphères, Milieux, Observations Spatiales/University of Versailles Saint Quentin
UVSQ, Université Paris-Saclay
6 : Laboratoire inter-universitaire des systèmes atmosphèriques
Centre National de la Recherche Scientifique : UMR7583, Université Paris-Est Créteil Val-de-Marne - Paris 12, Université Paris Diderot - Paris 7, Institut national des sciences de l\'Univers, Institut national des sciences de l\'Univers, Institut national des sciences de l\'Univers
61 Av du général de Gaulle 94010 CRETEIL CEDEX -  France
* : Corresponding author

The Mars Organic Molecule Analyzer (MOMA) experiment onboard the ExoMars 2020 rover (Rosalind Franklin) will analyze the content in organic molecules present in samples collected at the surface and subsurface (down to 2 meters) of Mars. MOMA has two complementary analytical modes: Laser Desorption/Ionization-Mass Spectrometry (LDI-MS) and Pyrolysis-Gas Chromatography-Mass Spectrometry (Pyr-GC-MS). In addition to the pyrolysis analysis, three types of derivatization reagents which can be used to make the analysis of refractory and very polar compounds by increasing their volatility and protecting the labile chemical groups: N-methyl-N-tert-butyldimethylsilyl-trifluoroacetamide – MTBSTFA; dimethylformamide dimethyl-acetal - DMF-DMA; and tetramethylammonium hydroxide TMAH. TMAH works as a methylation agent boosting the cleavage of macromolecules, thereby methylating the products released from sample pyrolysis, and giving rise to improved detection by GC-MS. TMAH thermochemolysis can provide complementary informations about organic compounds such as amino acids, aliphatic and aromatic carboxylic acids, ect.. TMAH derivatization can increase the volatility of the nucleobases by decreasing the polarity of the labile molecules, which makes it easier to identify nucleic acids in the complex mixtures.

However, we know perchlorate are present at the subsurface of Mars and could oxidize and degrade organic molecules at high temperature during the pyrolysis. Then, the effect of perchlorate on the derivatization reagent TMAH, needs to be studied. The products of TMAH pyrolysis with and without calcium perchlorate at different heating rate (flash pyrolysis and ramp pyrolysis (at a heating rate of 35 °C/min) up to 600°C ) were analyzed. What's more, the reaction mechanism of TMAH pyrolysis with perchlorate was studied by step pyrolysis. Results showed that the products of TMAH at flash pyrolysis and MOMA ramp are different. In addition, the calcium perchlorate has low effect on the pyrolysis of TMAH when the content of calcium perchlorate less than 5 wt. %. Therefore, TMAH seems a good derivatization solvent for the detection of organic compounds on MOMA.


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