Laboratoire Génie des Procédés et Matériaux (LGPM), CentraleSupélec, University Paris-Saclay, Gif-sur-Yvette, France.
LATMOS/IPSL, UVSQ Université Paris-Saclay, Sorbonne Université, CNRS, Guyancourt, France.
Astrobiology. 2021 Mar;21(3):279-297. doi: 10.1089/ast.2020.2252. Epub 2020 Dec 11.
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°C·min 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 [ClO] 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.
火星有机分子分析仪（MOMA）和火星样本分析仪器（SAM）分别安装在 2022 年的 ExoMars 号和火星科学实验室漫游车上，能够检测有机物，并区分火星样本中潜在的生物成因有机物质和非生物成因有机物质。为了识别有机物，这两种仪器都利用热裂解-气相色谱与质谱联用技术，并且还使用四甲基氢氧化铵（TMAH）作为热化学解剂来提高有机物质的挥发性。然而，TMAH 热化学解的反应性和效率受到火星表面高氯酸盐钙的影响。在这项研究中，我们在不同的加热速率（快速热解和类似于 SAM 的斜坡加热速率为 35°C·min）下，确定了存在和不存在高氯酸盐钙时 TMAH 热解的产物。通过使用分步热解研究了高氯酸盐钙存在下 TMAH 热解的分解机制。此外，还研究了高氯酸盐钙（在火星相关浓度下）对 TMAH 热化学解回收脂肪酸的影响。结果表明，快速热解比类似于 SAM 的斜坡加热速率法产生更多种类和更多丰度的 TMAH 热化学解产物。当 [ClO]低于 10 重量百分比（wt%）时，高氯酸盐钙对 TMAH 降解没有明显影响。最重要的是，在实验室条件下，高氯酸盐钙的存在对 TMAH 热化学解回收脂肪酸的影响并不显著，这对于使用 SAM 和 MOMA 仪器在火星上通过 TMAH 热化学解检测脂肪酸是有希望的。
