Sample Analysis at Mars (SAM)

Instrument Overview

The Sample Analysis at Mars (SAM) suite in the MSL Analytical Laboratory is designed to address the present and past habitability of Mars by exploring molecular and elemental chemistry relevant to life. SAM addresses carbon chemistry through a search for organic compounds, the chemical state of light elements other than carbon, and isotopic tracers of planetary change.

SAM is a suite of three instruments: a Quadrupole Mass Spectrometer (QMS), a Gas Chromatograph (GC), and a Tunable Laser Spectrometer (TLS). The QMS and the GC can operate together in a GCMS mode for separation (GC) and definitive identification (QMS) or organic compounds. The mass range of the QMS is 2-535 Da. The TLS obtains precise isotope ratios for C and O in carbon dioxide and H and O in water. It also measures trace levels of methane and its carbon isotope ratio.

The three SAM instruments are supported by a sample manipulation system (SMS) and a Chemical Separation and Processing Laboratory (CSPL) that includes high conductance and micro valves, gas manifolds with heaters and temperature monitors, chemical and mechanical pumps, carrier gas reservoirs and regulators, pressure monitors, pyrolysis ovens, and chemical scrubbers and getters. The Mars atmosphere is sampled by CSPL valve and pump manipulations that introduce an appropriate amount of gas through an inlet tube to the SAM instruments.

The solid phase materials are sampled by transporting finely- sieved materials to one of 74 SMS sample cups that can then be inserted into a SAM oven and thermally processed for release of volatiles.

Scientific Objectives

See [MAHAFFY2008].

A central goal of the Mars exploration program of several nations is to search for evidence of extant or extinct life on Mars and investigate the ability of that planet to sustain life. Recent success of the National Aeronautics and Space Administration (NASA) and European Space Agency (ESA) missions to Mars give an unprecedented total in 2006 of four operating orbiting spacecraft and two operating surface landers at the red planet. Data from these missions are providing a wealth of new information and a new understanding of the present state of Mars and its history that provides an increasingly firm foundation for the study of its past and present habitability and its potential to sustain life. Of particular note is the discovery of vast Polar Regions, rich in near-surface water ice [BOYNTONETAL2002B], geologically recent fluid flows that formed gullies [MALIN&EDGETT2000], possible trace levels of the disequilibrium species methane in the Martian atmosphere [KRASNOPOLSKYETAL2004], and mineralogical and morphological evidence of aqueous alteration of surface materials [SQUYRESETAL2004].

As a significant step toward the search for life on Mars, the top level science goal for the MSL mission is to explore and quantitatively assess a potential habitat on Mars. Three major objectives and specific measurement sets for this mission were stated by NASA after an extended period of mission definition and iteration by groups of scientists and engineers working closely together. The objectives are to

• Assess the biological potential of at least one target environment (past or present) by determining the nature and inventory of organic carbon compounds, taking an inventory of the chemical building blocks of life (C, H, N, O, P, S), and identifying features that may record the actions of biologically relevant processes.
• Characterize the geology of the landing region at all appropriate spatial scales by investigating the chemical, isotopic, and mineralogical composition of martian surface and near-surface geological materials and interpreting the processes that have formed and modified rocks and regolith.
• Investigate planetary processes that influence habitability by assessing long-timescale (i.e., 4 billion year) atmospheric evolution processes and by determining the present state, distribution, and cycling of water and CO2.

These MSL objectives realize a subset of a larger set of priority measurement objectives for the long-term scientific exploration of Mars that have been defined and updated over a period of several years by the Mars Exploration Program Analysis Group (MEPAG).

The Chemical and Isotopic Composition of Martian Volatiles

A primary motivation for the search for organic molecules on Mars is to understand if there is molecular evidence of pre-biotic or biotic activity, perhaps preserved from more than several billion years ago when the martian climate may have been much more Earth-like, with a thicker atmosphere, warmer surface temperatures, and persistent lakes or oceans. On Earth, tectonic recycling largely destroys molecular signatures of early life. In contrast, the more rapid cooling of Mars may have quenched such recycling and enabled preservation of early biotic or pre-biotic chemistry. For example, if preserved amino acids were found in Mars sedimentary deposits, their distribution could suggest a biotic or abiotic source mechanism. On the other hand, oxidants such as superoxide radicals [YENETAL1999], reactive surface complexes such as oxidized halides [ZENT&MCKAY1994], or radiation processing [KMINEK&BADA2006] may have transformed or destroyed martian organic molecules, thus reducing the diversity of such compounds from an earlier era and our ability to describe an early chemical history. Galactic cosmic rays penetrate only meters into the martian surface. Thus, it is possible that organics from an early wet Mars that may have been buried by aqueous, aeolian, impact, or volcanic transport of material and only recently exposed, may provide prime sites for the MSL search for organic molecules. Recent orbital spectroscopic evidence of phyllosilicates formed by aqueous alteration [BIBRINGETAL2006]; [MURCHIEETAL2007] has revealed several prime targets for a MSL landing site and for the MSL search for organic molecules.

Early exogenous sources of organics on Mars from carbonaceous asteroids and comets are expected to be similar to those that may have seeded Earth with pre-biotic compounds. These compounds may have been important in the origin of life on Earth. An estimated IDP influx of 106 to 107 kg/year resulting in several to tens of percent of the total mass of the Martian regolith has been predicted [FLYNN&MCKAY1990] and recent models [BLAND&SMITH2000] have predicted that meteorites greater than 10 grams are likely to be more abundant on Mars than any place on Earth, including the Antarctic meteorite-rich blue ice fields. These authors predict hundreds to hundreds of thousands of small meteorites delivered per square kilometer. The Ni enrichment in the bright dust observed by the MER chemical investigations has been described [YENETAL2005] as consistent with 1.2% contribution from chondritic (CI) meteoritic material. Although C-chondrites contain most of their carbon in a kerogen-like macromolecular form [CRONINETAL1998], they also contain a wide range of extractable compounds including amino acids, nucleobases and many other compound types [BOTTA&BADA2002]. Distributions of compounds or their oxidation products such as carboxylic acids that might plausibly be direct products of chondritic material might suggest that extensive biological production and processing of carbon compounds did not take place.

The Search for Organics in the Atmosphere of Mars

The Mariner 9 infrared spectrometer was able to obtain spectra in the 200 to 2,000 cm-1 (5-50 micrometer) spectral range for nearly a year in 1971 and 1972 and establish substantially reduced upper limits [MACGUIRE1977] for methane, ethane, ethylene, and acetylene shown in Table 1. More recent reports of methane mixing ratio observed from ground-based or from Mars Express are also listed in this table. It should be noted that due to the very low methane abundance, these detections are very near the sensitivity limit of both the orbital and ground-based instruments.

Table 1 Organic species mixing ratios or upper limits in the martian atmosphere

Species	Reported mixing ratio	Notes or upper limit (UL)
CH4	10 ppb (+/-5)	[FORMISANOETAL2004B], Mars Express PFS, average reported, variation between 0 and 30 ppb observed
CH4	UL = 20 ppb	[MACGUIRE1977], Mariner 9 IR spectrometer
CH4	11 ppb (+/-4)	[KRASNOPOLSKYETAL2004], ground-
CH4	UL = 7 ppb	based [VILLANUEVAETAL2006]
C2H6	400 ppb	[MACGUIRE1977], Mariner 9 IR spectrometer
C2H4	500 ppb	[MACGUIRE1977], Mariner 9 IR spectrometer
C2H2	2 ppb	[MACGUIRE1977], Mariner 9 IR spectrometer
CH2O	3 ppb	[KRASNOPOLSKYETAL1997]
CH2O	<5x10-7	[KORABLEVETAL1993], tentative detection / Phobos

No atmospheric organics were reported by the Viking entry mass spectrometer at an altitude of approximately 135 km [NIERETAL1976] or the Viking Gas Chromatograph Mass Spectrometer [BIEMANNETAL1976] from the surface of Mars.

The Search for Organics in Solid Phase Martian Materials

The focus of the Viking mission was to determine if there was life on Mars. In addition to the specific life-detection experiments designed to measure microbial metabolism [KLEINETAL1976]; [OYAMAETAL1977]; [LEVIN1997] that are discussed in this volume [SCHUERGER&CLARK2007], one of the primary science objectives of the Viking GCMS [ANDERSONETAL1972]; [BIEMANN1974] was to search for organic molecules or other volatiles released in pyrolysis of Martian fines to up to 200 deg C, 350 deg C, or 500 deg C that might be associated with microbial life. The sensitivity of the Viking GCMS for those organic molecules that could be transmitted through its GC column and through a palladium hydrogen separator to its 12-200 dalton magnetic sector mass spectrometer was a function of the attenuation of the gas directed into the mass spectrometer. This gas flow was limited during portions of the GC run to prevent saturation of the small vacuum ion pump. However, during the most sensitive period of operation, the Viking GCMS system would have been able to detect molecules at the several parts per billion (mass ratio to solid sample heated). Nevertheless, no organic molecules attributed to a Martian source were identified by either lander from either surface samples or from samples collected several centimeters below the surface by the Viking arm and scoop.

The negative Viking GCMS result for organic molecules can be qualified by the following observations: (1) the sensitivity of the GCMS for light organic molecules was reduced by a factor of ~1,000 for light molecules by the design of the gas-processing system that protected the vacuum ion pumps; (2) several classes of polar organic molecules such as carboxylic acids that are likely oxidation products [BENNERETAL2000] of aliphatic and aromatic hydrocarbons would not have been transmitted through the Viking GC column; (3) the Viking sample-acquisition system could only sample loosely consolidated fines instead of less permeable materials that might have been better protected from atmospheric oxidants. Nevertheless, these results provide motivation to use the extraordinary remote sensing tools presently available from orbital platforms to identify sites that are better candidates than the Viking landing sites for preservation of organic molecules that can be safely be accessed by a mobile landing platform. No surface organic molecules have been identified, to date, from orbit.

Several studies have been directed at identification of organics in meteorites that were likely removed from Mars by impact ejection [MCSWEEN1994]. These include reports of polycyclic aromatic hydrocarbons (PAHs) in the Antarctic martian meteorite ALH 84001 [MCKAYETAL1996] detected by resonance ionization time-of-flight mass spectrometry and the organic volatile products benzene, toluene, C2 alkylbenzene, and benzonitrile detected by pyrolysis GCMS in Nakhla [SEPHTONETAL2002]. No organic pyrolysis products were detected by the later authors in their samples of ALH 84001 while EET A79001 was also found to release aromatic organics. The extent of terrestrial contribution to the organic material Martian meteorites is necessarily a primary concern in this type of study and has received considerable attention for PAHs [BECKERETAL1997]; [CLEMMETTETAL1998], amino acids [BADAETAL1998], and for acid-insoluble organic material [JULLETAL2000]. Approaches to understanding the extent of terrestrial contamination can include analysis of the environment from where the meteorite was collected, a search for molecules expected to be produced abiotically, and precision carbon and hydrogen isotope measurements.

Distinguishing Sources of Martian Organics

One source of organic compounds delivered to Mars is certainly meteoritic and interplanetary dust particle infall. Organic compounds contained in these materials would be expected to be present in the martian regolith in the absence of their chemical oxidation in the martian surface environment. If a sufficiently rich suite of organic molecules are detected on Mars, both the distribution of chemical structures and isotopic composition will be employed to help establish their source. Organic molecules produced abiotically in space and exposed to radiation processing show distinct structural and isotopic characteristics. For example, they exhibit more highly branched carbon chain structures than those organic compounds that are the products of biological processes and exhibit a more uniform variation of abundance with molecular weight. For extraterrestrial organic matter delivered to Earth, differences in the stable carbon and hydrogen isotope ratios are also used as a tool to help distinguish these organics from the often dominating terrestrial organic matter. Although carbon isotopes alone may not provide sufficient discrimination, these measurements-combined with other information such as the D/H ratio and the structural information-can often provide a good indication of their extraterrestrial origin [SEPHTON&BOTTA2005]. The classes of organic compounds delivered to Mars from space may resemble those found in meteorites delivered to Earth, some of which are rich in organic compounds. For example, in the Murchison (CM2) carbonaceous chondrite a wide range of compound classes are found. These include more than 80 amino acids, nucleobases, sugar-related compounds, polycyclic aromatic hydrocarbons, carboxylic acids, as well as alcohols, aldehydes, ketones, and aliphatic and aromatic compounds [SEPHTON&BOTTA2005]. A primary objective of the SAM investigation will be to determine if these compound types are preserved in the near-surface materials in the chemical environment of the MSL landing site. Life on Earth imprints specific patterns in molecular structure, such as an enhancement in linear vs. branched carbon chains, specific chirality, and even/odd enhancements produced by enzymatic processing [SUMMONSETAL2007]. On Earth extant life can be distinguished by homochirality of the amino acid building blocks of proteins. One of the six SAM GC columns will have the capability to separate a number of chiral species, such as amines. In addition to structural patterns imprinted on sets of organic molecules during their formation, environmental processing results in evolution of these patterns [EIGENBRODE2008]. If sufficient abundance of organic molecules are present, the patterns in molecular structure will be diagnostic of their source. In this preliminary phase of exploration of the abundance of organics on Mars, the focus of the SAM GCMS experiment is to identify the widest possible range of organic compounds within the constraints of our pyrolysis and our substantially more limited one-step solvent extraction and derivatization processing. Of particular concern for martian organic analyses is terrestrial contamination. Organic compounds derived from Earth could be introduced to the samples before or during in situ sample acquisition and processing by the MSL and could potentially compromise the analysis of martian organics. Thus, the MSL science and engineering teams are working to mitigate this potential problem through a multi-pronged approach. Organic materials such as lubricants and epoxies used in the construction of the MSL systems are screened and whenever possible analyzed using similar pyrolysis GCMS techniques to those that will be employed on the surface of Mars. Materials that will contact or come in close proximity with the martian samples during acquisition and processing are most carefully selected and analyzed. A plan has been formulated to employ witness plates to collect organic materials emanating from MSL components during all stages of its assembly and qualification. Inside the SAM suite, the cells that will accept samples can be heated to ~1,000 deg C prior to sample delivery to drive off residual organic materials that might have migrated to its surfaces.

Several organic free blanks spiked with an easily identified fully fluorinated molecule are planned to be processed inside the SAM suite and occasionally through the entire sample manipulation system of the rover. This experiment will establish the level of contamination picked up during mechanical processing to produce the fine-grained material used by SAM and the fluorinated molecule will provide an externally delivered standard as a check on both sample delivery integrity and instrument performance. For practical reasons, the budget for terrestrial contamination is set at low parts per billion for several organic compound classes of greatest interest (e.g., benzene or aromatic hydrocarbons, 8 ppb; carbonyl or hydroxyl compounds, 10 ppb; amino acids, 1 ppb; amines or amides, 8 ppb; non-aromatic hydrocarbons, 8 ppb) although the sensitivity of the GCMS for stable organic compounds that evolve during pyrolysis and that transmit through the GC column is sub-parts per billion for a well-baked mass spectrometer analyzer. The target upper limit for total terrestrial reduced carbon in any MSL-processed sample delivered to SAM is 40 ppb. If organic molecules are not abundant at the MSL landing site, the definitive identification as indigenous to Mars of trace species detected will depend on how well the MSL developers are able to meet this contamination requirement.

Methane on Mars

Several of the various Mars atmospheric methane mixing ratios or upper limits that have been reported from both ground-based observations [VILLANEUVAETAL2006]; [KRASNOLOPSKYETAL2004] and from the Planetary Fourier Spectrometer PFS on the Mars Express spacecraft [FORMISANOETAL2004B] are shown in Table 1. Methane is a potential biomarker because it can be produced from extant or extinct microbial sources, but there are also plausible abiotic methane sources including serpentinization at depths of several kilometers below the martian surface, volcanic emissions, or exogenous delivery from primitive bodies such as cometary sources. While analysis of the likelihood of each of these sources continues to be analyzed [ATREYAETAL2006]; [KRASNOPOLSKY2006], it is clear that a considerably improved data base regarding methane source locations and temporal variability is needed to understand the sources and sinks of methane on Mars. Both the PFS and the ground-based data suggest a spatial and temporal variability that may indicate that the source flux is much greater than the fluxes suggested by the average mixing ratio and the predicted photochemical destruction rate.

It has been suggested that atmospheric chemistries [ATREYAETAL2006] that are the consequence of dust storm or dust devil electric field induced reactions [DELORYETAL2006] can produce the oxidant H2O2 in sufficient abundance to precipitate onto the martian surface. This oxidant could contribute to the destruction of reduced carbon compounds delivered by IDP and meteoritic infall to the martian surface and, in fact, this atmospheric chemistry driven by the dust devils and dust storms might also provide a sink for atmospheric methane. Identifying the sources and sinks of H2O2 could be critically important for understanding organic preservation in the martian environment.

Instrument Description

SAM's instruments are a Quadrupole Mass Spectrometer (QMS) from NASA Goddard, a 6-column Gas Chromatograph (GC) from the SAM French partners, and a 2-channel Tunable Laser Spectrometer (TLS) from the Jet Propulsion Laboratory. Gas Chromatography Mass Spectrometry implemented with integrated GC/QMS operation enables definitive identification of organic compounds to sub part-per- billion sensitivity while the TLS obtains precise isotope ratios for C, H, and O in carbon dioxide and water and measures trace levels of methane and its carbon 13 isotope [WEBSTERETAL2010]. The solid phase materials are sampled by transporting sieved materials delivered from the MSL sample acquisition and processing system to a sample cup of the Sample Manipulation System (SMS) that can then be inserted into one of 2 ovens for thermal processing and release of volatiles for chemical and isotopic analysis. Nine other hard sealed cups contain liquid solvents and chemical derivatization agents that can be utilized on Mars to extract and transform polar molecules such as amino acids, nucleobases, and carboxylic acids into compounds that are sufficiently volatile to transmit through the GC columns. Six other cups contain calibration materials to be used in situ. The SAM Chemical Separation and Processing Laboratory (CSPL) consists of valves, heaters, pressure sensors, gas scrubbers and getters, traps, and gas tanks used for calibration or combustion experiments [MAHAFFY2012].

QMS Calibration

The SAM QMS utilizes 6-inch hyperbolic rods. A three frequency RF circuit enables a mass range of 2-535 Da with m/z values selected by DAC control of the AC and RF amplitude and DC bias on the rod pairs. The high, medium, and low RF frequencies cover the mass ranges of 2-19, 20-149, and 150-535 respectively. Thus the parent peaks of the major Mars atmospheric gases are found in the mid frequency scan region with fragment peaks in the high frequency scan region. The electron emission from the filament of the electron gun of the QMS ion source is controllable by SAM command in the 2 - 200 micro-Amp range and the detector is a high gain channeltron operated in a pulse counting mode. The detector saturates as it approaches 10 million ions/second and a detector dead time correction of the form o = n exp(-tau n) where o represents the observed counts and n the corrected count rate represents the data well up to the point where the detector counts begin to decrease with increasing ion current. The best fits to the calibration data are obtained with tau itself set to be a function of o (tau = a exp(b o) where a and b are constants determined by securing the best linear fit to the count rate at a selected m/z with pressure. Independent of the electron multiplier, a faraday cup can also be utilized at high ion currents to extend the dynamic range of the QMS [MAHAFFYETAL2012]; [FRANZETAL2011].

Most of the SAM Flight Model (FM) calibration experiments were carried out in the chamber that was developed for SAM environmental testing. This chamber generates the range of temperatures and pressures expected at Mars and utilizes a 4-component Mars gas mix. Gas manifold lines are introduced through the chamber wall to enable separate introduction of calibration gases and to provide exhaust-pumping lines. A subset of calibration runs was carried out with SAM out of the chamber. Although many calibration runs were carried out with a mixture of gases in the predicted Martian composition, a mixture with approximately equal volumes of these 4 gases was used to establish the instrument response [MAHAFFYETAL2012].

Doubly charged ions or fragments can also provide a suitable reference signal when a parent ion is saturated. The calibration exercise described has established a set of calibration constants to enable rapid conversion of such ratios secured from SAM on Mars into atmospheric volume mixing ratios. The calibration gas delta-13C has been independently determined in our laboratory and independent calibration of the other isotope ratios in these gases is planned.

Operational Considerations

SAM is designed to measure volatile trace-gas species, including atmospheric gases or organics thermally or chemically extracted from solid-phase materials, such as rocks or fines. Three fundamentally different approaches are employed for the measurement of organics in solids delivered to SAM by the sample acquisition/ sample preparation and handling unit (SA/SPaH).

Pyrolysis

The primary method for the detection of organic molecules by SAM is pyrolysis. This approach samples the gas thermally evolved from a small aliquot of sample delivered from the SA/SPaH to one of the quartz cups of the sample manipulation system. Each quartz cup can accommodate up to 0.5 cm^3 of sample and the incremental volume of sample delivered from the SA/SPaH is approximately 0.05 cm^3. This enables a specified volume of sample to be delivered to a cup and possible reuse of cups in an extended mission by deposition of fresh sample on the devolatilized residue in a cup. For direct analysis via the QMS or TLS, the sample in the quartz cup is heated from ambient to ~1,000 deg C with a programmable temperature ramp. As gases are released, they are swept through the gas manifold by a helium carrier gas for detection by the spectrometers. Typically, water of hydration is released from samples early in the temperature ramp. Moderately volatile organics are released in the 300 deg C to 600 deg C region due to thermal desorption and the breakdown of macromolecular organic matter. At higher temperatures, gases evolve due to the further pyrolysis of refractory organics and the breakdown of minerals. For example, carbonates and sulfates thermally dissociate to CO2 and SO2, respectively, at temperatures greater than 500 deg C. The temperature at which minerals degrade is often diagnostic of the mineral type. In addition to direct analysis of the evolved gases, there is an option in SAM to direct the gas flow over a high-surface-area adsorbent to trap organic molecules, thus separating organic from inorganic volatiles for subsequent analysis by GCMS. Passing the trapped and released organic volatiles through one of six GC columns effectively separates different molecules allowing for individual detection in the QMS. As a consequence of pyrolysis, the complex refractory organic molecules embedded in a mineral matrix or thermally unstable species may break down during thermal processing to produce lower molecular weight or more stable pyrolysis products. Thus, information on the parent organic molecules must be inferred from the patterns of stable products evolved with temperature. For example, pyrolysis of microbial material typically evolves amines, but the more fragile amino acids are destroyed [GLAVINETAL2006]. Although the performance of the flight version of the SAM GCMS is not yet established, our tests on the SAM prototype instrument suggests that limit of detection will be ~10e-14 to 10e-13 mole depending on compound and instrument background. The mass range of the QMS is 2-535 dalton to sample a wide range of organic compounds.

Combustion

The second tool used by SAM to understand the state of carbon in Mars rocks and fines is combustion. Reduced carbon in samples delivered to the SAM sample cups is planned to be oxidized by stepped combustion using isotopically pure 16O2 and analyzed in the QMS and the TLS for the 13C/12C ratio in the CO2 product. The 13C/12C ratio in organic matter is used as a biomarker on Earth because organisms prefer the lighter 12C isotope and typically incorporate 2-4% more 12C into their cells than is present in the CO2 carbon source. The utility of these measurements will depend on the ability of SAM to reveal the isotopic composition of the most important reservoirs of inorganic carbon for comparison with organic carbon. Two such reservoirs are the atmosphere itself and carbonates that may also be found in the rocks or sedimentary materials that MSL may be able to sample. The combined evolved gas and atmospheric sampling should enable this comparison.

Solvent Extraction and Derivatization

In addition to the dry pyrolysis experiments, a small number of SAM sample cups are dedicated to a simple single-step solvent extraction and chemical derivatization process. Resource constraints of MSL preclude a more ambitious fluid extraction and analysis approach. Depending on the chemistries encountered in Mars rocks and soils, this technique may be effective in enabling an analysis of several classes of molecules that could be of biotic or prebiotic relevance including amino acids, amines, carboxylic acids, and nucleobases. Without derivatization these compounds would not elute from the columns of the gas chromatograph under the protocols applied on SAM. Extraction of the organics from the powdered sample delivered to the SAM cells employs dimethylformamide (DMF) and the derivatization agent is a silylation reaction utilizing N,N-Methyl-tert-butyl (dimethylsilyl) trifluoroacetamide (MTBSTFA). The selected volumes of derivatization agent and solvent are mixed together during the SAM integration and then hard-sealed into a metal cup. The top of the cup consists of an electron-beam welded foil that can be punctured on the surface of Mars using the vertical motion of the sample cup into a foil puncture station. The cup is then placed under the SAM sample inlet tube so that these fluids can be mixed with the Mars powdered sample. The cup is next delivered to the pyrolysis station where the desired reaction temperature (~80 deg C) in the sample is set. The hard seal into the pyrolysis chamber ensures that vapor does not escape to space during this reaction time. After several tens of minutes of reaction, much of the solvent is evaporated to space through a microvalve and a heated vent tube and the chemical products produced by the derivatization reaction are flash heated into the injection traps of the gas chromatograph.

The SAM team has exposed the selected solvents and derivatization agents to more radiation than would be expected over the course of the mission to ensure that the radiation-induced chemistry is negligible over the nominal SAM mission. While it is possible that excessive water in the Mars sample or silylation side reactions with salts or clays may substantially compromise the detection of amino acids and carboxylic acids, this 'one-pot' extraction/derivatization method has been successfully applied by the SAM team [BUCHETAL2006] to several terrestrial Mars analogs including low-bioload Atacama samples previously studied by pyrolysis and other techniques [NAVARRO-GONZETAL2003]. The volume of the SAM wet cells enables a substantial excess of derivatization agent to be supplied that will mitigate the impact of side reactions. An internal standard (a fluorinated amino acid compound in a separately punctured dry chamber) will allow us to evaluate if these undesired side reactions have fully or partially prevented the reaction with the organics of interest. See [BUCHETAL2006] for a preliminary report on the development of the protocol used in SAM and its application to Atacama Mars analog samples.