Derivatization and Thermochemolysis Treatment aboard the MOMA experiment

Abstract

International audienceThe Mars Organic Molecule Analyzer (MOMA) experiment onboard the ExoMars 2020 rover will analyze the content in organic molecules present in samples collected at subsurface of Mars. MOMA has two complementary analytical modes : Laser Desorption/Ionization-Mass Spectrometry and Pyrolysis-Gas Chromatography-Mass Spectrometry. In addition to the pyrolysis analysis, three types of derivatization reagents are present in twelve capsules and can be used to anamyse the 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. MTBSTFA is the most versatile reagent. It is dedicated to analyze the labile compounds with a very high sensitivity. DMF-DMA preserves the chiral center of molecules and will allow their enantiomeric separation. TMAH will be used to extract and characterize the potential refractory compounds (macromolecules, kerogen, etc.) and protect polar compounds (alkylation) released from the pyrolysis experiment. MOMA operates under severely constrained resources which directly influence the ultimate instrument performance. The restrictions on mass, power and data volume limit the mass range, resolution and duty cycle of the instument compared to a laboratory one and impact the available options for sample treatment. This is why we have developed capsules dedicated to chemical extraction by derivatization. To test the feasibility and the efficiency of the sample treatment using our capsules we have mimicked the MOMA procedure. We have filled six capsules of each reagents. Then we have tested the opening temperature of each capsule and tested the efficiency of sample treatment with our capsule. We have used standard solutions of several chiral amino acids and non-chiral carboxylic acids. We have shown that the selected capsule eutectics allowed the reagents to be released at the right temperatures. Also we have found that the efficiency of derivatization and thermochemiolysis was identical both for laboratory experiments and MOMA like derivatization with capsules. This result verifies the method that will be used on Mars to analyze the soil and rock samples to be collected by the rover