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A. Buch, R. Sternberg, D. Meunier (U. Paris 12 et 7 (LISA) - CNRS), C. Szopa (Service d'Aéronomie (SA), UMR CNRS, Inst. Pierre Simon Laplace (IPSL)), M. Cabane (Service d'Aeronomie (IPSL CNRS), U. Pierre et Marie Curie (PARIS VI)), F. Raulin (U. Paris 12 et 7 (LISA) - CNRS), P. Mahaffy (NASA GSFC)
In situ analysis of carboxylic and amino acids on Mars by solvent-extraction and chemical derivatization coupled to gas chromatography
In the frame of the SAM (Sample Analysis at Mars) project (for Mars Science Laboratory, MSL 2009) , we have developed a space instrument sub-system, based on gas chromatography, for the in situ analysis of some of the "key prebiotic" organic molecules expected to be contained in the Martian soil. This analysis is carried out following three steps : extraction of the organic matter from the soil, derivatization of the organic extracted compounds, and GC-MS analysis.
To develop this system, samples from the driest and wettest parts of the Atacama desert in Chile (R. Navarro-Gonzalez ), currently considered by now as the best analogues of the Martian soil for the exobiological point of view, were used in this study as a reference material.
We have first selected and optimized the best solvent for the extraction step of the targeted molecules. Although water is the best solvent for amino acids, it cannot be used since it is an important molecule targeted by several in situ experiments. Moreover water is not appropriate for all the carboxylic acids, especially for derivative benzoic carboxylic acids expected to be present at the Martian surface . For this reason, an alternative solvent was searched by the comparison of the performances of a wide range of solvents. We have thus shown that 2-propanol was the best solvent for the extraction of both family of the targeted compounds. In order to lower the energy consumption and especially the time needed for each analysis, ultrasonic assisted extraction was carried out. Three major parameters of extraction were studied : time of extraction, temperature and volume of solvent contacted with the soil. The results showed that the use of ultrasonication allowed to decrease the extraction time from 24 h (heating in oven at 100 °C) to 30 min. at room temperature with a significant increase of the extraction yield.
Finally the derivatization step procedure, based on silylation reaction [3, 4], was also optimized. The effect of the sonication and the quantity of the derivative reactant on the derivatisation reaction time and yield were also determined. This system was shown to be the most efficient for the detection of the low concentration levels (ppm) amino and carboxylic acids of the Atacama desert samples . It is thus expected to be the most efficient for the in situ analysis of organics in the Martian soil.
 Navarro-Gonzalez R. et al. Mars like soils in the Atacama desert. Submitted
 S. A. Benner, K. G. Devine, L.N. Matveeva, D.H. Powel PNAS 97(6) (1998) 2425- 2430
 C . Rodier, R. Sternberg, F. Raulin, C. Vidal-Madjar, J. Chromatogr. A 915 (2001) 199.
 Buch, R. Sternberg, D. Meunier, C. Rodier, C. Laurent, F. Raulin and C. Vidal-Madjar, J. of Chromatogr. A, 999, (1-2), (2003) 165-174
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.