In Situ Analysis of the Martian Regolith Using Solvent Extraction and Chemical Derivatization

Mars is presently the most likely planet on which there is a possibility of finding extinct and/or extant life. Future exploratory missions to Mars in search of evidence for life will focus on key organic molecules such as carboxylic and amino acids. The 2009 Mars Science Laboratory (MSL) Mission will offer an opportunity to carry out in situ measurements for organic compounds on Mars. Gas chromatography mass spectrometry (GC-MS) is one technique that will be proposed for MSL. We are currently developing an automated extraction process coupled to chemical derivatization in order to target several key organic compounds using GC-MS. This paper presents a solid-liquid extraction method (1) that can be coupled with in situ GC-MS analyses of organic compounds on Mars. Amino acid and carboxylic acid extraction efficiencies from a soil sample collected from the Atacama Desert, Chile (2) using several different organic solvents including (isopropanol and water) have been determined. We found that a 1:1 mixture of isopropanol and water was the best solvent with high extraction yields for both amino and carboxylic acids in less than 30 minutes when the extraction procedure is assisted by ultrasonic treatment. A highly sensititive and quantitative single-step derivatization reaction was carried out using N-methyl, N-tert.-butyl (dimethylsilyl) trifluoroacetamide (MTBSTFA) as the silylating agent prior to GC-MS analysis. The effect of pH and salt concentration on the derivatization reaction was also studied. We have also demonstrated the feasibility of carrying out extraction and derivatization directly on the soil in a one-step procedure The development of a miniaturized reactor, where both the extraction and the derivatization processes could take place is currently under investigation. This method is discussed for an easy automation with coupling to an in situ GC-MS space instrument. (1) A. Buch et al., J.of Chrom. A, 999 (2003) 165-174 (2) R. Navarro-Gonzàlez et al., Science 302 (2003) 1018-1021