Instrument Overview
  ===================
 
    The Sample Analysis at Mars (SAM) suite in the MSL Analytical
    Laboratory is designed to address the present and past
    habilitability 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 actylene 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.