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

Abstract

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 -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 [ClO 4 -] 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.

In situ organic biosignature detection techniques for space applications

“…Perhaps most importantly, TMAH appears to be better suited for samples containing perchlorates. He et al (2021b) demonstrated that up to 5 wt% of calcium perchlorate did not significantly impact the recovery of free fatty acids at a concentration of 300 ppb. In situ analysis with TMAH at Mars has been performed; however, data analysis is, at this moment, ongoing (Roach et al, 2021).…”

“…Limited validation of the one-pot methodologies for COSAC, SAM, or MOMA has been published. Nonetheless, a multitude of demonstration and qualitative studies have been performed with flight-like sample chambers coupled to commercial GC-MS systems where pyrolysis, derivatization, or thermochemolysis were applied (e.g., Lewis et al, 2018;Reinhardt et al, 2020;He et al, 2021b). Whereas the one-pot derivatization methodology is versatile, it also adds risk.…”

The application of TMAH thermochemolysis on the detection of nucleosides: Applications for the SAM and MOMA instruments

“…The SAM-like ramp pyrolysis is the same as in previous work [32,33]. In this process, a cup containing the sample was heated using heart-cut EGA temperature zones from 50 °C to reach the final temperature (850 °C held for 1 min) at the SAM heating rate of 35 °C min -1 .…”

Planetary Mass Spectrometry for Agnostic Life Detection in the Solar System

“…Both of these approaches are currently being employed by SAM onboard the Curiosity rover as part of the MSL mission (Mahaffy et al, 2012;Williams et al, 2019;Millan et al, 2021, accepted) and by the MOMA instrument (Goesmann et al, 2017;Mißbach et al, 2019;Reinhardt et al, 2020). Some methods (e.g., derivatization approaches) may be sensitive to some salts and water (Freissinet et al, 2015;Mißbach et al, 2019) while others (e.g., TMAH thermochemolysis) are more tolerable of both (Mißbach et al, 2019;He et al, 2021). Thus, sample matrix composition for Martian and other astrobiology targets, particularly the briny, ice-covered oceans harbored by moons of the outer planets, may require instruments to adapt new hardware, methods, and operations for salt-laden samples (e.g., addition of desalting or dilution steps).…”