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Laser ablation-miniature mass spectrometer for elemental and isotopicanalysis of rocksM. P. Sinha, E. L. Neidholdt, J. Hurowitz, W. Sturhahn, B. Beard et al. Citation: Rev. Sci. Instrum. 82, 094102 (2011); doi: 10.1063/1.3626794 View online: http://dx.doi.org/10.1063/1.3626794 View Table of Contents: http://rsi.aip.org/resource/1/RSINAK/v82/i9 Published by the American Institute of Physics. Related ArticlesNote: Programmable data acquisition system for research measurements from meteorological radiosondes Rev. Sci. Instrum. 83, 036106 (2012) Balloon-borne disposable radiometer for cloud detection Rev. Sci. Instrum. 83, 025111 (2012) The effects of patch-potentials on the gravity probe B gyroscopes Rev. Sci. Instrum. 82, 074502 (2011) A new x-ray interface and surface scattering environmental cell design for in situ studies of radioactive andatmosphere-sensitive samples Rev. Sci. Instrum. 82, 075105 (2011) A versatile facility for laboratory studies of viscoelastic and poroelastic behaviour of rocks Rev. Sci. Instrum. 82, 064501 (2011) Additional information on Rev. Sci. Instrum.Journal Homepage: http://rsi.aip.org Journal Information: http://rsi.aip.org/about/about_the_journal Top downloads: http://rsi.aip.org/features/most_downloaded Information for Authors: http://rsi.aip.org/authors

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REVIEW OF SCIENTIFIC INSTRUMENTS 82, 094102 (2011)

Laser ablation-miniature mass spectrometer for elementaland isotopic analysis of rocks

M. P. Sinha,1,3,a) E. L. Neidholdt,1 J. Hurowitz,1 W. Sturhahn,1 B. Beard,2,3 andM. H. Hecht11Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr, Pasadena,California 91109, USA2Department of Geology and Geophysics, 1215 W. Dayton St., University of Wisconsin-Madison,Madison, Wisconsin 53706, USA3NASA Astrobiology Institute, USA

(Received 10 June 2011; accepted 1 August 2011; published online 14 September 2011)

A laser ablation-miniature mass spectrometer (LA-MMS) for the chemical and isotopic measurementof rocks and minerals is described. In the LA-MMS method, neutral atoms ablated by a pulsed laserare led into an electron impact ionization source, where they are ionized by a 70 eV electron beam.This results in a secondary ion pulse typically 10–100 μs wide, compared to the original 5–10 ns laserpulse duration. Ions of different masses are then spatially dispersed along the focal plane of the mag-netic sector of the miniature mass spectrometer (MMS) and measured in parallel by a modified CCDarray detector capable of detecting ions directly. Compared to conventional scanning techniques, si-multaneous measurement of the ion pulse along the focal plane effectively offers a 100% duty cycleover a wide mass range. LA-MMS offers a more quantitative assessment of elemental compositionthan techniques that detect ions directly generated by the ablation process because the latter can bestrongly influenced by matrix effects that vary with the structure and geometry of the surface, thewavelength of the laser beam, and the not well characterized ionization efficiencies of the elementsin the process. The above problems attendant to the direct ion analysis has been minimized in theLA-MMS by analyzing the ablated neutral species after their post-ionization by electron impaction.These neutral species are much more abundant than the directly ablated ions in the ablated vaporplume and are, therefore, expected to be characteristic of the chemical composition of the solid. Also,the electron impact ionization of elements is well studied and their ionization cross sections are knownand easy to find in databases. Currently, the LA-MMS limit of detection is 0.4 wt.%. Here we describeLA-MMS elemental composition measurements of various minerals including microcline, lepidolite,anorthoclase, and USGS BCR-2G samples. The measurements of high precision isotopic ratios in-cluding 41K/39K (0.077 ± 0.004) and 29Si/28Si (0.052 ± 0.006) in these minerals by LA-MMS arealso described. The LA-MMS has been developed as a prototype instrument system for space appli-cations for geochemical and geochronological measurements on the surface of extraterrestrial bodies.© 2011 American Institute of Physics. [doi:10.1063/1.3626794]

I. INTRODUCTION

Chemical and isotopic measurements of rock and soilsamples on extraterrestrial bodies have the potential to ad-dress an enormous range of scientific questions. Rocks andsoils contain the geological record of the internal and exter-nal processes that shaped the evolution of their parent body;a record that can be read through measurements of chemi-cal composition, isotopic composition, and age.1 Measure-ment of the abundances of radiogenic parent-daughter isotopepairs provides the absolute age of the rocks in which these el-ements occur and thus, the timeline of the planet’s formationand modification. There is currently no means to perform suchradiogenic isotope analysis remotely from planetary surfaces,and age estimates are limited to statistical techniques basedon counting impact craters in images of planetary surfaces.2–5

The only means of assessing the absolute age of planetary sur-faces is through radiometric dating analysis of meteorites in

a)Author to whom correspondence should be addressed. Electronic mail:[email protected].

terrestrial laboratories.6, 7 Details of the provenance of suchmeteorites is speculative at best (i.e., little is known of wherethey originate from on the planetary body from which theywere derived). It is therefore difficult, if not impossible, to re-late radiometric ages from meteorites and their complemen-tary chemical and isotopic compositions to specific geologicfeatures and place them into the context provided by analysisof the relative chronostratigraphy of a planetary surface.8–11

In situ measurements of chemical and isotopic compo-sition, and radiometric age, tied to spatially resolved min-eralogical and textural features, of rocks and soils can pro-vide important constraints on geological processes and eventsthat are the subject of intense interest in the planetary sciencecommunity, such as the nature and timing of sedimentary rockforming processes and the role of liquid water in the early his-tory of the planet Mars.12–15 To that end, we have developed anovel laser ablation-miniature mass spectrometer (LA-MMS)instrument to make these in situ geological measurements.The paper describes the instrument, its methodology, and theresults of measurement of elemental and isotopic composition

0034-6748/2011/82(9)/094102/7/$30.00 © 2011 American Institute of Physics82, 094102-1


http://dx.doi.org/10.1063/1.3626794http://dx.doi.org/10.1063/1.3626794http://dx.doi.org/10.1063/1.3626794mailto: [email protected]

094102-2 Sinha et al. Rev. Sci. Instrum. 82, 094102 (2011)

of various rocks. Isotopic ratio measurements may eventuallyenable in situ radiometric age dating of rock and mineral sam-ples using the K–Ar or Rb–Sr methods. Our aim is to developa laboratory prototype of LA-MMS instrument for space mis-sions, in particular to Mars, for such measurements that maybe deployable on a rover or lander.

II. EXPERIMENTAL

A. Methodology

LA-MMS comprises: (1) sampling of minerals by laserablation (LA); (2) electron impact ionization (EI) of the ab-lated neutrals; and (3) their mass spectral measurement bya miniature mass spectrometer (MMS). Developed at the JetPropulsion Laboratory (JPL), the MMS features a double fo-cusing focal plane geometry, and a modified CCD array iondetector.

LA allows a sample to be introduced into the MMSwith minimal requirements on sample manipulation andpreparation.16 A high-energy laser pulse incident on the solidsample produces a plume of ions and neutrals. In principle,chemical and isotopic analysis of either the ions or the neutralspecies can reveal the composition of the source rock. How-ever, laser ablation produces two to six orders of magnitudemore neutrals than ions,17 and does so with minimal selec-tivity for particular species. In contrast, ion generation by ab-lation is dependent on matrix effects associated with surfacecomposition, geometry, and texture; elemental ionization en-ergies; and properties of the laser beam. Consequently, anal-ysis of neutrals in the ablated plume is more likely to yield arepresentative composition than analysis of ions. The rate ofcreation of neutrals and the volume of the analyzed samplecan be adjusted by varying the energy and the spot diameter(typically 10-100 μm) of the laser pulse. Thus, it is possibleto select individual mineral grains for analysis, or to measurea bulk average.

In addition to EI, post-ionization of laser ablated neutralspecies may be accomplished by resonant photo-ionization(RI), nonresonant photo-ionization, or by inductively coupledplasma (ICP). RI offers specificity for a selected element, en-hancing contrast, but requires a unique laser for each elementsampled. The efficiency of the RI process is also not as wellcharacterized as EI, which allows calibration by measurementof the relative concentration of different elements.18, 19 A ver-sion of this method, laser ablation time-of-flight resonanceionization mass spectrometry (LA-TOF-RIMS), is being de-veloped elsewhere for Rb–Sr geochronology.20 Finally, whileLA-ICP-MS is widely applied to high sensitivity elementaland isotopic analysis, the high power and mass requirementsof such an instrument make its application to space difficult.21

In the LA-MMS instrument, ablated neutral species areanalyzed for elemental and isotopic concentration. Neutralatoms are ionized by EI, a well-characterized process witha known probability of ionization of the various chemicalspecies. EI is widely used for mass spectrometry for spaceapplications.22 While EI is often applied to the ionization oflaser-ablated neutrals,23 the short duration of the secondaryion pulse (typically 10–100 μs)24 and the relatively low laser

repetition rate (5 Hz in the current instance) make a scanningtype of MS less suitable than an instrument that can measurethe entire mass distribution simultaneously. Though time-of-flight mass spectrometers are often coupled to laser ablationsystems, they require a much shorter duration ion pulse (10−8

to 10−9 s) to achieve the time separation of different massions in the flight path. By measuring masses in parallel with amodified CCD based direct-ion detector array, LA-MMS ef-fectively offers a 100% duty cycle for each mass during theion pulse measurement.

B. Instrument details

Figure 1 shows the schematic of the LA-MMS system.The rock sample and the MMS are housed in separate cham-bers that are pumped differentially by turbo molecular pumps.A plate having a 2 mm diameter aperture in the center sepa-rates the sample chamber from the MMS chamber. The sam-ple is placed at a distance of about 10 cm from the plate andthe ion source of the mass spectrometer is located at a distanceof 3.8 cm on the far side of the plate. The operating pressuresin the sample chamber and the MMS chamber are maintainedat 2 × 10−6 and 1.1 × 10−7 Torr, respectively.

A pulsed Nd-YAG laser (Continuum Surelite III, Con-tinuum, Santa Clara, CA) operating in Q-switched mode(1064 nm wavelength, 5 ns pulse width, and 200 mJ energyper pulse) is focused on the rock sample for ablation with a200 mm focal length lens placed outside the sample chamber.The laser beam has an angle of incidence of ∼30◦ to the sam-ple surface, which limits operation to shallow ablation pitsunless the beam is rastered. The laser spot size is estimatedto be 800–1000 μm (based on the size of the ablation pit),corresponding to a power density of (5–8) × 109 W cm−2 onthe sample surface. The plasma generated by a laser shot isshown in Fig. 2.

FIG. 1. Schematic of the experimental setup of LA-MMS. A Nd-YAG laseris focused at the sample at ∼5 Hz repetition rate. After removal of the ablatedions by electrostatic deflection, a fraction of the ablated vapor plume con-taining neutral species reaches the EI source of the MMS. The signal ions,generated by the post-ionization of the neutrals in the ion source, are sepa-rated spatially according to their masses along the focal plane of the magneticsector of the MMS and measured by the 2140-element CCD detector array.



FIG. 2. (Color online) Photograph of the laser ablated plasma. The ablatedplume is peaked forward in the direction normal to the sample surface.

The vapor plume is peaked in the direction normal to thesample and expands through a pair of electrostatic deflectionplates (900 V potential difference, 2.5 cm separation) in orderto remove the ablated charged particles that otherwise tend tocause charging of the ion optical elements. The ablated neu-tral species are sampled through a 2 mm hole into the ionsource, which is of the DuPont design,25 where they are sub-jected to a thermionic beam of electrons for ionization. Themass analyzer of the MMS is of the double sector focal planedesign (Mattauch-Herzog geometry). Details of the design aswell as a smaller version of the analyzer with a 2.5 cm focalplane have been described previously.26 A photograph of theminiaturized mass analyzer and the detector array are shownin Fig. 3.

The analyzer has an electrostatic sector with a 7.6 cm ra-dius of curvature, and a magnetic sector with a 5 cm focalplane, and a field strength of 0.9 T between the pole pieces.Ions formed by electron impact in the ion source are acceler-ated to the object slit to an energy of 1050–1100 V and in-jected into the electrostatic and magnetic sectors, where theyare spatially separated by mass along the focal plane of the

FIG. 3. (Color online) Photograph of the miniature mass spectrometer. TheCCD detector array and its electronics board are mounted along the 5 cmfocal plane of the magnetic sector.

magnetic sector. The ion path radii within the magnet lie inthe range 2.5 cm ≤ rion ≤ 6.1 cm. The detectable mass rangeis defined by an upper limit Mmax and a lower limit Mmin suchthat the ratio, Mmax/Mmin = 6. The CCD direct-ion detectorarray is mounted on a copper block and attached to a liquidnitrogen cooled cold finger with a metal strap. During massspectral measurement the detector is cooled to ∼−25 ◦C.

A slit, consisting of two electrically isolated semicircularsegments, precedes the magnetic sector to help shape the ionbeam and to serve as an electronic shutter. When both halvesof the slit are at ground potential, the slit allows the passageof ions through the magnetic sector and on to the detector;when one slit half is held at 70 V the beam is deflected anddoes not enter the magnetic sector. Ions generated from back-ground gases in the chamber are eliminated from being in-tegrated by the detector past the duration of laser ablated-EIionized signal pulse by opening the shutter for only a shorttime following the laser pulse. This also reduces the vacuumrequirements.

The distribution of ions along the focal plane is measuredsimultaneously for the duration of the neutral/ion pulse by amodified CCD array developed at JPL. Each of the 2140 pix-els in the one-dimensional array is 20 μm wide in the dis-persion direction and 2000 μm tall.27 The conventional CCDphotodetection elements on each pixel have been replaced bymetal-oxide-semiconductor (MOS) capacitors that integratethe charges of impinging ions during the exposure. Each ionsensing element (MOS capacitor) is coupled to the CCD shiftregister by means of a “fill-and-spill” input structure that cre-ates a packet of signal charge proportional to the charge on thecapacitor.28 The combination of the MMS analyzer and theCCD array enables extremely efficient use of the signal andis uniquely suited for isotopic measurements of laser ablatedneutral pulses. A commercial implementation of the detectorarray is available from ITT Analytics’ OI Analytical, CMSField Products, Pelham, AL.

C. Signal measurement timing sequence

The ion signal accumulation timing sequence is shown inFig. 4. At the start of the signal integration time specified inthe data acquisition software, a trigger pulse is sent to fire theflash lamp of the Nd-YAG laser. The trigger pulse is also fedinto an electronic pulse generator, which produces additionaltrigger pulses for the flash lamp, the Q-switch and the sig-nal acquisition. The laser is Q-switched 225 μs after the flashlamp begins firing, and is synchronized with the grounding ofthe ion entrance slit, effectively opening an electronic shutterto allow ions to enter the magnetic sector. The shutter is heldopen for 300 μs which, for the typical laser repetition periodof 212 ms, corresponds to a collection duty cycle of 1:700 forions arising from the background gases while collecting100%of the laser ablation signal. To minimize read noise, the signalis accumulated in the detector for a frame that spans multiplelaser shots. For the measurements presented here, this integra-tion interval was 5 s, or 23 laser shots. Each frame contains theaccumulated charge recorded by the 2140 detector elements,and multiple frames are combined to create a spectrum. Aftereach readout the detector requires a 2.7 ms reset time.



FIG. 4. The timing diagram of laser firing and ion gating at the entrance slit of the magnetic sector. The Nd-YAG laser flash lamp is fired at 212 ms intervalsand the laser is Q-switched 225 μs later, producing a 5 ns laser pulse. One half of the slit is normally kept at 70 V, deflecting ions produced in the EI ionizationsource away from the slit opening. The ions pass through this electronic shutter for 300 μs subsequent to the laser pulse when this half of the slit is grounded.

III. RESULTS AND DISCUSSION

We have demonstrated the performance of the LA-MMSby measuring the chemical and isotopic analysis of vari-ous minerals and a United States Geological Survey (USGS)glass geochemical reference material. The analytical samplesincluded microcline (empirical formula KAl(Si3O8)), lepi-dolite (empirical formula KLi2AlSi4O10(F,OH)2), anortho-clase (empirical formula Na0.75K0.25AlSi3O8), and the USGSBCR-2G. The microcline was from a “pink microcline testchip pack” obtained from Ward’s Natural Science, Rochester,NY, and was originally collected near Madawaska, Ontario,Canada. The sample of lepidolite was from the author’s (B.Beard) collection that was also obtained from Wards Scien-tific and originally had been collected from Minas Gerias,Brazil. The anorthoclase, hosted in a rock collected near Oslo,Norway that also includes probable mica, olivine, Fe–Ti ox-ide, and Ca–phosphate, is from the rock and mineral col-lection of the California Institute of Technology (Caltech),Division of Geological and Planetary Sciences (GPS). Bothfeldspar samples contain exsolved lamellae of Na-feldspar, acommon feature of natural alkali feldspars. For an indepen-dent assessment of composition, the same samples were an-alyzed with a JEOL 8200 electron microprobe located in theCaltech GPS Division Analytical Facility. Polished thin sec-tions of each sample were prepared and carbon coated usingstandard practices. The electron microprobe is equipped withfive wavelength dispersive spectrometers. Analytical condi-tions were an accelerating voltage of 15 kV, beam current of25 nA, a 10 μm beam spot size, and an integration time of40 s. Standards were checked at the beginning of the analyti-cal session and found to be within 1% of their known values.Chemical concentrations in BCR-2G were obtained from theUSGS Certificate of Analysis supplied with this geochemicalreference material.

A. Elemental analysis

Figure 5 shows the mass spectra resulting from the laserablation of the four samples. Each spectrum is an averageof 50 frames of the CCD ion detector array, each acquiredwith a 5 s integration time, for a total of 1150 laser shots.A background spectrum, acquired by running the same se-quence without the laser firing, was subtracted from the signalspectrum.

A single mass peak is typically spread over 10 CCD pix-els, as seen in Fig. 5. Figure 6 shows the intensity of severalelemental peaks for the BCR-2G reference material, each rep-resenting a sum of the channels under the peak, relative to thatof silicon. These values are seen to compare favorably to theUSGS-provided values.

The intensities were corrected for difference in the elec-tron impact ionization cross sections for the elements. Weobserve excellent agreement for the relatively more volatileelements (K, Na), while the LA-MMS technique appears tounder-sample more refractory species. This is likely due tosome combination of elemental fractionation in laser ablation,preferential attrition of species during transmission from thesample chamber to the MMS ion source, and space charge ef-fects, and can possibly be addressed through calibration. Toaddress fractionation associated with ablation, we are inves-tigating the use of shorter laser wavelengths by doubling orquadrupling the fundamental output of the Nd-YAG laser. In-vestigations using LA-ICP-MS have found that while elemen-tal fractionation depends both on laser parameters and on thephysical and chemical properties of the sample, the effect islessened as the size of the laser ablated particle decreases withthe use of shorter laser wavelengths, approaching the ideal ofpure atomic vaporization. At shorter wavelengths, the laserlight is reported to couple better to most minerals, minimiz-ing fractionation.29, 30



FIG. 5. Mass spectra of laser ablated species from, (a) USGS BCR-2G, (b) anorthoclase, (c) lepidolite, and (d) microcline measured by the MMS. Each spectrumis an average of 50 frames, each of which represents 23 laser shots over 5 s.

The close agreement for K is encouraging for our primaryobjective of using LA-MMS for K–Ar age dating. The excel-lent agreement between the observed/measured values of K/Sifor different minerals can be seen in Fig. 7.

The larger difference between the LA-MMS measuredvalue for K/Si ratio and the e-probe measured value foranorthoclase relative to the other analyzed samples may beattributed to the characteristics of the sample observed in oure-probe measurement. We observed that the sample does notconsist of a single mineral phase. Consequently, the relativelylarge spot size of the ablation laser on the sample may resultin the ablation of multiple K bearing mineral phases, someof which have higher or lower K/Si ratios compared to thatof anorthoclase. In this case, it would appear that we havesampled a K-rich phase (probably mica, with a K/Si ratio of∼0.45) that has biased our LA-MMS results to a higher thanexpected K/Si ratio (Fig. 5(b)). In the future, higher spatialresolution on the target sample will be achieved by decreas-ing the spot size of the laser pulse.

Figure 8 plots the intensities of K (series 2) and Si(series 1) measured by LA-MMS for microcline against therespective number of laser shots, demonstrating that the in-tegrated intensity of a mass peak increases linearly withthe number of laser shots used to generate the signal. Thisdemonstrates that, for shallow pits, the LA-MMS yield is notstrongly dependent on the evolving pit geometry.

B. Isotopic measurements

Table I lists the stable isotope ratios 41K/39K, 29Si/28Si,and 30Si/28Si for the minerals microcline, lepidolite, andanorthoclase measured by LA-MMS. Because these are stableisotopic ratios that are generally not subject to significant frac-tionation during geological processes on Earth, they shouldnot vary from mineral phase to mineral phase. Therefore, wehave chosen to show the average plus or minus 1σ for all threemineral phases. These values are found to be in good agree-ment with the reference/literature values that demonstrate the



FIG. 6. (Color online) Measured elemental composition of BCR-2G relativeto silicon also measured by the LA-MMS is plotted against the correspondingUSGS reference values.

FIG. 7. (Color online) The K/Si ratios of the minerals measured by LA-MMS are compared with the corresponding values determined by the analysisof the same samples using a JEOL 8200 electron microprobe.

FIG. 8. (Color online) Variation of integrated intensities of K, and Si, withthe number of laser shots.

TABLE I. Isotopic ratios of K and Si measured by LA-MMS on microcline,lepedolite, and anorthoclase. A close agreement of these values with the nat-ural abundance ratios is found.

Isotope ratios LA-MMS measured values Natural abundance ratios

41K/39K 0.077 ± 0.004 0.073929Si/28Si 0.052 ± 0.006 0.050930Si/28Si 0.034 ± 0.004 0.0335

viability of the LA-MMS method for the isotopic analysis ofminerals. The values of one standard deviation for the isotopicratios are also listed in Table I that demonstrate the high re-producibility even with the limited number of measurements.However, we were unable to measure the isotopic compo-sition for potassium in BCR-2G sample due to the limitedsensitivity of the method at the present time. LA-MMS canpresently analyze elements in samples with >0.4% total con-centration by weight.

IV. SUMMARY AND APPLICATIONS

We have developed a novel method of chemical and iso-topic analysis of solid samples. It has been demonstrated thatthe LA-MMS instrument can quantitatively determine the ele-mental composition of solid sample at a concentration level of>0.4%. The novelty of the method lies both in the sampling ofneutral ablated material and in the simultaneous measurementof all the elemental species. The 100% duty cycle of the focalplane geometry of the mass analyzer with the direct ion detec-tor array enables highly efficient, hence rapid measurement ofa small volume of ablated material. Work is in progress to en-hance the sensitivity of the LA-MMS method to allow mea-surement of elements at lower concentrations in mineral/rocksamples. First, the geometry of the sample location, the laserincidence angle, and the injection of the ablated vapor into theion source will be improved. These changes will lead to theionization of a larger fraction of the ablated vapor plume. Atpresent, the sample is located at a distance of ∼13.8 cm fromthe ion source and the ablated plume is sampled into the MMSchamber through a 2 mm diameter hole in the plate 10 cmfrom the sample site, separating the MMS chamber and thesample chamber. A new design, currently being implemented,is expected to increase the efficiency of sampling by morethan an order of magnitude (×10) by bringing the sample towithin ∼3 cm of the ion source and by increasing the angle ofincidence of the laser to the substrate to near normal. Second,the sensitivity of the CCD detector element is being improvedby addition of an amplification stage using ion to electronconversion and modification of the CCD to operate in an elec-tron detection mode. Presently, the read noise is equivalent toabout ∼500 ions per pixel. With the above improvements, weexpect to reduce the limit of detection from ∼0.4% to ppmlevels.

This LA-MMS can be miniaturized to meet the require-ments of a rover based spacecraft instrument for applicationsto various NASA missions with minimal technology devel-opment. Besides the electronics and data system (similar inkind to those used for experiments such as TEGA on NASA’s2007 Phoenix Mars mission), the major components of the



instrument consist of (1) the mass spectrometer, (2) the laser,and (3) pumping and its housing subsystem. The miniatur-ization of the mass spectrometer in MMS is already welladvanced and operational (Fig. 2). The laser being used forthe ChemCam instrument on the NASA 2011 Mars ScienceLaboratory (MSL) mission is adequate for laser ablation inLA-MMS.31 A diode-pumped passively Q-switched mi-crochip may also be a choice for space applications. Com-mercially available miniature turbo molecular drag pumps(Creare, Inc., Hanover, NH) are also being used on the MSLmission as part of the SAM instrument.

ACKNOWLEDGMENTS

The authors thank Shannon Jackson for technical sup-port in the design and implementation of some of the elec-tronics for the LA-MMS. The development of LA-MMS wasperformed at the Jet Propulsion Laboratory (JPL), CaliforniaInstitute of Technology and was supported by grants from theNational Aeronautics and Space Administration. The researchwork described in this paper was, in part, supported by theNASA Astrobiology Institute (NAI).

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