Measuring Perchlorate and Sulfate in Planetary Brines using Raman

Sep 11, 2018 - Lauren E McGraw , Nina McCollom , Charity M Phillips-Lander , and Megan E Elwood Madden. ACS Earth Space Chem. , Just Accepted ...
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Measuring Perchlorate and Sulfate in Planetary Brines using Raman Spectroscopy Lauren E McGraw, Nina McCollom, Charity M Phillips-Lander, and Megan E Elwood Madden ACS Earth Space Chem., Just Accepted Manuscript • DOI: 10.1021/ acsearthspacechem.8b00082 • Publication Date (Web): 11 Sep 2018 Downloaded from http://pubs.acs.org on September 12, 2018

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Measuring Perchlorate and Sulfate in Planetary Brines using Raman Spectroscopy Lauren E. McGraw, Nina D. S. McCollom, Charity M. Phillips-Lander, Megan E. Elwood Madden* School of Geology and Geophysics, University of Oklahoma, Norman, OK, USA 73019 * corresponding author, melwood@ou.edu KEYWORDS: Raman Spectroscopy, Planetary Protection, Brine, Mars, Europa, Aqueous Solutes Abstract: Liquid water likely exists on the surface of Mars and below the icy crusts of Europa, Enceladus, and Titan. Pluto, Ceres, and Ganymede also show evidence of liquid water at or near the surface. Quantitative solute analyses would provide critical data needed to understand geochemical conditions throughout our solar system, including potential habitability of planetary bodies. We have developed and tested a Raman spectroscopic method for measuring perchlorate and sulfate in brines and dilute waters that utilizes simple Raman peak height ratios rather than peak area ratios. Ratios of the target anion and OH- bending water peaks yield linear fits with positive slopes and r2 values >0.99. Calibration fits for each solute-brine combination and ultrapure water yield similar linear equations, suggesting this method can detect and quantitatively measure solutes in complex aqueous solutions. No sample preparation or physical contact with the sample is required. Therefore, this method can be employed without contaminating the fluid or the spacecraft.

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Introduction

Due to the extremely low temperatures and vapor pressures on most planetary surfaces, brines are the most likely host for liquid water in many planetary environments because salts lower both the freezing point and vapor pressure(1,

2, 3, 4, 5, 6, 7, 8)

. Indeed, slope streaks and

recurring lineae on Mars likely contain salts that may be deposited through evaporation of brines(9,

10)

and Enceladus’ water plumes have been shown to contain dissolved salts(11,

12, 13)

.

These solutes observed in brines may provide key clues to determine the geochemical conditions, including habitability of the environments in which they are found, both on Earth and other planets(14, 15, 16, 17, 18). However, brines are difficult to analyze using standard methods even in a terrestrial laboratory without significant dilution. High solute concentrations can overwhelm detectors and the brines themselves are often corrosive with relatively high densities and viscosities, which can clog traditional aqueous analytical tools and/or contaminate subsequent samples. Therefore, novel analytical tools and techniques are needed to measure solutes in brines on potentially habitable planetary bodies. Optical analytical methods that require little or no sample preparation and allow analysis from a distance, without physical contact with the instrument, could prevent corrosion, while also maintaining strict planetary protection protocols. Raman spectroscopy identifies phases and species by using an excitation laser to probe molecular vibrations within the target. Spectra acquired through a spot analysis can be used to identify both the structure and composition of the material, allowing solids, liquids, gases, and dissolved species to be identified in situ. Multiple spectra measured over a sample area or time extends this application to mapping and time-series analyses. Raman spectrometers have been previously employed in terrestrial laboratory studies to determine the composition of ancient

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water samples trapped in fluid inclusions(e.g. 19, 20, 21,22,23,24,25), map the secondary mineralogy of meteorites(e.g.

26, 27)

, identify salt deliquescence and hydration states under Mars-analog

conditions(28, 29, 30, 31, 32), measure CO2 solubility in MgSO4 brines analogous to fluids expected on Europa and other icy moons(32,

33)

, observe deep ocean chemistry and mineralogy(34,

measure solutes within sea ice veins(37, 38), and detect Archaea(39,

40)

35, 36)

,

and other signs of life in

terrestrial evaporite deposits(41, 42 43, 44, 45, 46). Abundant research has documented Raman’s utility in detecting extant or fossil biomolecules in rocks and sediment(e.g.

47, 48, 49, 50, 51, 52, 53, 54)

. However, very few studies have investigated

potential Raman methods for detecting/measuring solutes in brines despite recent studies documenting modern brines on or near the surface of Mars and other habitable bodies in the Solar system. Unlike most traditional methods for measuring aqueous solutes, Raman spectra can be collected remotely (no physical contact with the sample) without sample preparation. Therefore, aqueous samples can be analyzed without contacting the instrument which could lead to clogging and corrosion issues. Remote analysis of aqueous samples also provides a mechanism for collecting important data regarding habitability, while also preserving planetary protection protocols. Therefore, Raman may be the ideal technique for analyzing planetary fluids on potentially habitable worlds. This versatility led to incorporation of Raman spectrometers on both the upcoming ExoMars(55, 56) and Mars 2020 rover missions(57, 58). Previous Raman studies have focused on measuring aqueous components in relatively dilute solutions(e.g. 59, 60, 61,62,63,64). For example, both Wu and Zheng(64) and Sun and Quin(63) measured carbonate anions in solution by comparing the primary carbonate peak (1066 cm-1) to the dominant OH-stretching peak at ~2750-3900 cm-1 using low-spectral resolution gradings to collect data over a wide spectral range. Murata et al. (1999) also determined sulfate

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concentrations in brackish NaCl solutions by adding perchlorate as an internal standard and comparing the spectrally close sulfate (981 cm-1) and perchlorate (934 cm-1) peaks. Other studies(e.g. 59, 61, 65) focused primarily on determining detection limits for aqueous ions. In this study, we aim to develop and test Raman spectroscopy as a viable technique for measuring perchlorate and sulfate concentrations in NaCl-, Na2SO4-, and NaClO4-bearing planetary fluids by comparing anion peaks with the O-H bending region for water near 1640 cm1

. We chose to target perchlorate and sulfate salts because both anions have been observed

directly on the surface of Mars and may provide important information regarding the geochemistry and habitability of extant and ancient waters. Chloride, sulfate, and perchlorate brine matrices represent likely endmember brines on Mars and other planetary bodies, including Europa, Enceladus, and Ceres. We focused on the water OH-bending region from 1400-1800 cm1

,

centered at 1640 cm-1 as an internal standard because both sulfate (981cm-1) and perchlorate

(934 cm-1) have strong Raman peaks nearby, allowing for direct comparison of normalized peak ratios using a high-resolution grating.

Methods Stock aqueous solutions containing known concentrations (0

to 1 m) of research grade

NaClO4 and Na2SO4 were prepared using 18 MΩ ultrapure water (UPW) and subsequently mixed in 1:1 ratios with stock solutions of 5.7 m NaCl, 2 m NaClO4, or 0.35 m Na2SO4 brine or ultrapure water to form standard solutions for Raman analysis. The perchlorate standards were mixed with UPW, NaCl brine, or Na2SO4 brine, while sulfate standards were mixed with UPW, NaCl brine, or NaClO4 brine. We chose to use all sodium salts in these experiments so that we

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could directly measure anion concentrations, without any potential cation interferences. All measurements were conducted at 295-298K and 1 atm. We collected a Raman spectrum for each standard solution using a green, 532 nm wavelength, 100 mW diode laser coupled with a Renishaw InVia Reflex Raman mapping microscope. The laser was focused through a Leica 50x objective lens into a 1 ml liquid sample held in a ceramic painter’s pallet (Supporting Information Figure 1). We operated the laser in streamline mode to raster the laser beam through a larger volume of the sample. We used a grating with 2400 grooves per centimeter centered at 1200 cm-1 to collect the Raman spectra between 850cm-1 and 1750 cm-1. All spectra from the NaCl and NaClO4 brines and UPW were collected at 100% laser power for 100 seconds, while the Na2SO4 spectra were collected at 100% laser power for 20 seconds to avoid overloading the charge coupled detector (CCD). We collected multiple accumulations such that each sample experienced 300 seconds of laser exposure. The high power, long collection time, and multiple accumulations increased the signal/noise ratio. The lower collection time for the sodium sulfate samples resulted in more noise than observed in the other solutions, but the intensity was sufficient for accurate measurements. Using the WiRE4.2 software package, we processed the spectra by manually picking minima points along the curve and used a linear or polynomial equation between those points to subtract the baseline. After subtracting the baseline, we normalized each spectrum to the highest peak observed. We then used WiRE 4.2’s curve-fitting tool to determine the peak heights, positions, and areas. We compared the height and area of each target anion peak with the O-H bending water region observed at 1640 cm-1 by calculating peak height and peak area ratios. While this O-H bending region is composed of two overlapping O-H bending vibration bands(66), we chose to model the spectra as one peak for the purpose of this study. We plotted the model peak height

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and peak area ratios against the known solute concentrations to determine a calibration curve for each solute-matrix tested. In order to determine the reproducibility and error associated with our measurements, we also conducted two replicate experiments. In the first experiment, we collected six sequential spectra of 0.5 ml 0.1 m NaClO4 standard solution mixed with 0.5 ml UPW. Each set of six spectra were collected over ~ 1 hour and measured on the same 1 ml sample. Following this experiment, we also mixed 10 ml of the 0.1 m Na2SO4 standard solution with 10 ml UPW, then pipetted a 1 ml subsample onto the ceramic palette and immediately collected a spectrum. We repeated this process for a total of 6 spectra collected from each 1 ml sample immediately after pipetting. Following each of these measurements the spectra were processed using the methods described above to determine peak height and peak area ratios (Supporting Information, Table 2). Results and Discussion Raman spectra collected from Na2SO4 and NaClO4 standards mixed with UPW, 5.7 m NaCl, 0.35 m Na2SO4, or 2 m NaClO4 show systematic increases in peak height as the standard concentration increases (Figure 1, Table 1). The major sulfate peak observed at 981 cm-1 is clearly delineated from the major perchlorate peak at 935 cm-1 in mixed perchlorate-sulfate brine and sulfate-perchlorate brine experiments. In addition, the broad water peak centered at 1640 cm1

decreases in relative intensity as solute concentrations increase. In each stock brine solution, the

sulfate/water and perchlorate/water peak ratios remain relatively constant, as demonstrated in the spectra collected from Na2SO4 standards mixed with 2 m NaClO4 brine and NaClO4 standards mixed with 0.35 m Na2SO4 brine (Figures 1b and 1e), suggesting that changing the concentration of either ions in solution does not systematically affect target solute peak intensity ratios.

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Peak height ratios comparing the dominant sulfate peak (981 cm-1) to the 1640 cm-1 O-H bending peak, show a linear relationship between 0-1 m concentration with a high correlation coefficient (r2 > 0.99), yielding a calibration equation (Figures 2a and b) of

   = 0.029±0.0011 ∗  − 0.0045±0.0062,

(Eq. 1)

where ε1 is the 981/1640 peak height ratio. Likewise, the ratio comparing the dominant perchlorate peak (935 cm-1) to the 1640 cm-1 O-H bending peak, also shows a linear relationship between 0-1 M concentration with a high correlation coefficient (r2 > 0.99), yielding a calibration equation (Figure 2c and d) of

  = 0.029±0.0028 ∗  − 0.0072±0.0014,

(Eq. 2)

where ε2 is the 935/1640 peak height ratio. Peak height ratios measured for both Na2SO4 and NaClO4 standards are highly reproducible. Replicate 1 ml samples of the 0.1 m Na2SO4 standard yield a peak height ratio standard deviation of ± 5%. Similar standard deviations were also observed for repeated measurements of the same sample of 0.1 m NaClO4 standard over a period of over 1 hour, demonstrating that laser heating and evaporation did not affect the Raman spectra (Supporting Information, Table 2). Previous studies used peak area ratios to determine the concentration of carbonate anions in aqueous solutions(63, 64); however, we found peak height ratios were consistently more reliable measures of anion concentration in our experiments. For example, while the 981/1640 cm-1 peak area ratios show a linear correlation at high sulfate concentrations, peak area ratios are not reliable indicators of sulfate concentration in standards less than 0.1 M (Figure 2c). In addition,

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peak area ratios are not indicative of perchlorate concentration across the full range of standards tested (Figure 2d). Therefore, peak height ratios are more effective measures of sulfate and perchlorate concentration than peak area ratios in these experiments. Raman spectroscopy is an excellent candidate for studying brines present on other planets, such as melting permafrost or Recurring Slope Lineae (RSL) on Mars and plumes emanating from Enceladus and Europa. The lack of sample preparation and remote measurement conditions make it an ideal measurement tool for unmanned rovers and landers. By studying planetary analog brines with differing solute concentrations, we have demonstrated that it is possible to use Raman spectroscopy to quantitatively determine solute concentration from analysis of a simple Raman spectrum. Future work is needed to fully investigate the effects of multicomponent brines and varying pH and temperature conditions on Raman spectra. Such measurements of aqueous anion concentration will provide planetary scientists with critical data required to better understand geochemical and atmospheric conditions, as well as potential habitability on other planetary bodies.

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Figure 1. Baseline-corrected and intensity normalized Raman spectra of Na2SO4 (a-c) and NaClO4 (d-f) standards mixed with UPW and 5.7m NaCl, 0.35m Na2SO4, or 2m NaClO4 brine matrices. The Raman band at 981 cm-1 increases as sulfate concentration increases in the Na2SO4 standards, while the band at 935 cm-1 increases as perchlorate concentration increases in the NaClO4 standards. The broad water peak centered at 1640 cm-1 decreases in relative intensity as the concentration of both solutes increases. Therefore, relative peak intensities can be used to measure solute concentrations in aqueous solutions. Small peaks observed at 1050, 1450, 1520,

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and 1555 cm-1 represent dissolved gases from the atmosphere and aromatic compounds likely released from the solution storage bottles.

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Figure 2. Calibration curves for Na2SO4 (A and C) and NaClO4 (B and D) salts using both peak height (A and B) and peak area (C and D) ratios. Grey boxes in the upper graphs show the area re-plotted in the lower graphs to better view data in the lower concentration (< 0.05M) samples.

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While peak height ratios show excellent R2 values at all concentrations, peak area ratios show low R2 values at low concentrations suggesting peak area ratios are not an effective measure of aqueous solute concentration.

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Table 1. Curve Fits from Raman Calibration Spectra Na2SO4 Concentration (m) in matrix standard Ultrapure Water 0.5 1 0.25 0.5 0.05 0.1 0.025 0.05 0.005 0.01 0.0025 0.005 0.0005 0.001 2 m NaClO4 Brine 0.5 1 0.25 0.5 0.05 0.1 0.025 0.05 0.005 0.01 0.0025 0.005 0.0005 0.001 5.7 mNaCl Brine 0.5 1 0.25 0.5 0.05 0.1 0.025 0.05 0.005 0.01 0.0025 0.005 0.0005 0.001 0 0

Peak Height 934

981

na na na na na na na

1.02 1.01 1.02 0.95 0.20 0.15 0.09

0.99 1.00 1.01 1.00 1.01 1.00 1.01 na na na na na na na na

NaClO4 Concentration (m) in matrix standard 934 Ultrapure Water 0.5 1 1.01 0.25 0.5 1.02 0.05 0.1 0.98 0.025 0.05 1.00 0.005 0.01 0.32 0.0025 0.005 0.25 0.0005 0.001 0.06 0 0 0.00 0.35 m Na2SO4 Brine 0.5 1 1.01 0.25 0.5 1.00 0.05 0.1 0.35 0.025 0.05 0.17 0.005 0.01 0.05 0.0025 0.005 0.04 0.0005 0.001 0.03 0 0 0.01 5.7 m NaCl Brine 0.5 1 1.01 0.25 0.5 1.01 0.05 0.1 0.99 0.025 0.05 0.99 0.005 0.01 0.29 0.0025 0.005 0.29 0.0005 0.001 0.14 0 0 0.07

Peak Area 1640

Peak Height Ratio

981

1640

0.06 0.13 0.43 0.77 0.99 0.98 0.99

10.48 10.45 10.96 12.59 2.20 1.65 0.99

9.48 21.61 66.69 119.84 153.01 174.08 158.54

17.47 7.77 2.38 1.24 0.20 0.15 0.09

1.11 0.48 0.16 0.11 0.01 0.01 0.01

0.90 0.41 0.10 0.02 0.00 0.01 0.00

0.05 0.04 0.05 0.04 0.05 0.05 0.02

9.80 4.21 0.76 0.19 0.00 0.05 0.00

20.08 6.67 9.52 5.94 8.32 6.61 1.64

17.61 9.82 2.05 0.57 0.00 0.12 0.00

0.49 0.63 0.08 0.03 0.00 0.01 0.00

1.01 1.01 1.01 1.00 0.29 0.06 0.13 0.00

0.06 0.11 0.30 0.80 1.01 0.99 1.00 0.99

11.28 11.29 12.11 11.22 45.27 2.13 2.52 0.01

8.08 14.58 45.27 96.67 130.27 125.75 125.75 140.00

16.62 9.55 3.35 1.25 0.29 0.06 0.13 0.00

1.40 0.77 0.27 0.12 0.35 0.02 0.02 0.00

Peak Height 981

Peak Area 1640

981/1640

Peak Area Ratio

Peak Height Ratio

934

1640

934/1649

981/1640

Peak Area Ratio 934/1640

na na na na na na na na

0.06 0.11 0.44 0.93 0.99 1.00 0.98 0.98

13.58 13.30 12.87 15.30 8.88 5.03 0.98 -0.03

15.33 22.27 76.04 170.74 172.41 174.14 158.85 153.45

16.51 9.43 2.23 1.08 0.32 0.25 0.06 0.00

0.89 0.60 0.17 0.09 0.05 0.03 0.01 0.00

0.36 0.66 1.01 0.98 0.99 1.01 1.01 1.01

0.05 0.10 0.14 0.14 0.13 0.14 0.14 0.13

13.67 13.12 4.57 2.00 0.61 0.63 16.87 0.18

11.46 22.32 24.09 23.93 20.83 23.59 23.00 20.94

19.12 9.80 2.44 1.20 0.35 0.26 0.21 0.09

1.19 0.59 0.19 0.08 0.03 0.03 0.73 0.01

na na na na na na na na

0.07 0.12 0.52 0.99 1.00 1.00 0.98 1.01

15.49 15.56 16.99 20.80 5.20 7.52 1.69 1.25

10.65 16.83 77.71 145.63 1.00 145.63 142.99 141.11

14.48 8.64 1.88 1.00 0.29 0.29 0.14 0.07

1.45 0.92 0.22 0.14 5.23 0.05 0.01 0.01

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AUTHOR INFORMATION Corresponding Author *Megan E. Elwood Madden * melwood@ou.edu Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding Sources This project was partially funded by NASA grant NNX13AG75G. The Raman system was purchased with funds from NSF MRI grant EAR1428857. LMM and NDSM acknowledge support from CPSGG’s undergraduate research program Supporting Information Tables 1a and b report the intensity versus wavenumber data for each spectra, Table 2 reports curve fits from the replicate spectra used to determine the standard deviations, and Figure 1 provides further information about the ceramic paint pallet used in the experiments ACKNOWLEDGMENT MEEM thanks Dr. Jennifer Shaiman and the 2016 GeoWriting class for their efforts collecting preliminary data. We also thank Associate Editor E. Herbst, K. Benison, M.-C. Caumon, and an anonymous reviewer for their comments which improved this manuscript.

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16. Yakimov, M.M.; La Cono, V.; Spada, G.L.; Bortoluzzi, G.; Messina, E.; Smedile, F.; Arcadi, E.; Borghini, M.; Ferrer, M.; Schmitt‐Kopplin, P.; Hertkorn, N. Microbial community of the deep‐sea brine Lake Kryos seawater–brine interface is active below the chaotropicity limit of life as revealed by recovery of mRNA. Environ. Microbio. 2015, 17(2), 364-382. 17. Stevenson, A.; Burkhardt, J.; Cockell, C. S.; Cray, J.A.; Dijksterhuis, J.; Fox‐Powell, M.; Kee, T.P; et al. Multiplication of microbes below 0.690 water activity: implications for terrestrial and extraterrestrial life. Environ. Microbio. 2015, 17(2), 257-277. 18. Wadsworth, J.; Cockell, C. S. Perchlorates on Mars enhance the bacteriocidal effects of UV light. Scientific Reports 2017, 7(1), 4662. 19. Frezzotti, M.L.; Tecce, F.; Casagli, A. Raman spectroscopy for fluid inclusion analysis. Journal of Geochemical Exploration 2012, 112, 1-20. 20. Bakker, R.J. Raman spectra of fluid and crystal mixtures in the systems H2O, H2O-NaCl and H2O-MgCl2 at low temperatures: Applications to fluid-inclusion research. Canadian Mineralogist 2004, 42, 1283-1314. 21. Benison, K.C.; Goldstein, R.H.; Wopenka, B.; Burruss, R.C.; Pasteris, J.D. Extremely acid Permian lakes and ground waters in North America. Nature 1998, 392, 911-914. 22. Pasteris, J.D. and Wanamaker, B.J. Laser Raman microprobe analysis of experimentally re-equilibrated fluid inclusions in olivine. Some implications for mantle fluids. American Mineralogist 1988, 73,1074-1088.

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23. Pasteris, J.D.; Wopenka, B.; Seitz, J.C. Practical aspects of quantitative laser Raman microprobe spectroscopy for the study of fluid inclusions. Geochimica et Comsopchimica Acta 1988, 52, 979-988. 24. Chou, I.M.; Pasteris, J.D.; Seitz, J.C. High-density volatiles in the system C-O-H-N for the calibration of a laser Raman microprobe: Geochimica et Cosmochimica Acta, 1990, 54, 535-543. 25. Chou, I.M., and Wang, A.L. Application of laser Raman micro-analyses to Earth and planetary materials. Journal of Asian Earth Sciences, 2017, 145, 309-333. 26. Ling, Z.;Wang, A. Spatial distributions of secondary minerals in the Martian meteorite MIL 03346,168 determined by Raman spectroscopic imaging. JGR-Planets 2015, 120, 1141-1159. 27. Hallis, L.J.; Taylor, G.J. Comparisons of the four Miller Range nakhlites, MIL 03346, 090030, 090032 and 090136: Textural and compositional observations of primary and secondary mineral assemblages. Meteoritics and Planetary Science 2011, 46, 1787-1803. 28.Nikolakakos,

G.;

Whiteway,

J.A.

Laboratory

investigation

of

perchlorate

deliquescence at the surface of Mars with a Raman scattering lidar. Geophys. Rsh. Lett. 2015, 42, 7899-7906. 29.Gough, R.V.; Chevrier, V.F.; Tolbert, M.A. Formation of aqueous solutions on Mars via deliquescence of chloride-perchlorate binary mixtures. EPSL 2014, 393, 73-82.

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30. Nuding, D.L.; Rivera-Valentin, E.G.; Davis, R.D.; Gough, R.V.; Chevrier, V.F.; Tolbert, M.A. Deliquescence and efflorescence of calcium perchlorate: An investigation of stable aqueous solutions relevant to Mars. Icarus 2014, 243, 420-428. 31. Gough, R.V.; Chevrier, V.F.; Baustian, K.J.; Wise, M.E.; Tolbert, M.A. Laboratory studies of perchlorate phase transitions: Support for metastable aqueous perchlorate solutions on Mars. EPSL 2011, 312, 371-377. 32. Wang, A.; Freeman, J.J.; Jolliff, B.L.; Chou, I.M. Sulfates on Mars: A systematic Raman spectroscopic study of hydration states of magnesium sulfates. Geochim. et Cosmochim. Acta 2006, 70, 6118-6135. 33. Bonales, L.J.; Munoz-Iglesias, V.; Prieto-Ballesteros, O. Raman spectroscopy as a tool to study the solubility of CO2 in magnesium sulphate brines: application to the fluids of Europa's cryomagmatic reservoirs. European J. of Mineralogy 2013, 25, 735-743. 34. White, S.N.; Dunk, R.M.; Peltzer, E.T.; Freeman, J.J.; Brewer, P.G. In situ Raman analyses of deep-sea hydrothermal and cold seep systems (Gorda Ridge and Hydrate Ridge). Geochem. Geophys. Geosystems 2006, 7. 35. Dable, B.K.; Love, B.A.; Battaglia, T.N.; Booksh, K.S.; Lilley, M.D.; Marquardt, B.J. Characterization and quantitation of a tertiary mixture of salts by Raman spectroscopy in simulated hydrothermal vent fluid. Applied Spectroscopy 2006, 60, 773-780 36. Dunk, R.M.; Peltzer, E.T.; Walz, P.M.; Brewer, P.G. Seeing a deep ocean CO2 enrichment experiment in a new light: Laser Raman detection of dissolved CO2 in seawater. Environ. Science & Tech. 2005, 39, 9630-9636

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37. Barletta, R.E.; Dikes, H.M. Chemical analysis of sea ice vein µ-environments using Raman spectroscopy. Polar Record 2015, 51(2), 165-176. 38. Geilfus, N‐X.; Carnat, G.; Dieckmann, G.S.; Halden, N.; Nehrke, G.; Papakyriakou, T.; Tison, J‐L.; Delille, B. First estimates of the contribution of CaCO3 precipitation to the release of CO2 to the atmosphere during young sea ice growth. J. of Geophys. RshOceans 2013, 118(1), 244-255. 39. Winters, Y.D.; Lowenstein, T.K.; Timofeeff, M.N. Identification of Carotenoids in Ancient Salt from Death Valley, Saline Valley, and Searles Lake, California, Using Laser Raman Spectroscopy. Astrobiology 2013, 13, 1065-1080. 40. Fendrihan, S.; Musso, M.; Stan-Lotter, H. Raman spectroscopy as a potential method for the detection of extremely halophilic archaea embedded in halite in terrestrial and possibly extraterrestrial samples. J. of Raman Spectroscopy 2009, 40, 1996-2003. 41. Vítek, P.; Jehlička, J.; Edwards, H. G. M.; Hutchinson, I.; Ascaso, C.; Wierzchos, J. Miniaturized Raman instrumentation detects carotenoids in Mars-analogue rocks from the Mojave and Atacama deserts. Phil. Trans. R. Soc. A 2014, 372(2030), 20140196. 42. Conner, A.J.;Benison, K.C. Acidophilic Halophilic Microorganisms in Fluid Inclusions in Halite from Lake Magic, Western Australia. Astrobiology 2013,13, 850860. 43. Jehlička, J.; Oren, A. Raman spectroscopy in halophile research. Frontiers in Microbio 2013, 4.

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44. Edwards, H. G.; Sadooni, F.; Vítek, P.; Jehlička, J. Raman spectroscopy of the Dukhan sabkha: identification of geological and biogeological molecules in an extreme environment. Phil. Trans. of the R. Soc. A 2010, 368(1922), 3099-3107. 45. Schallreuter, K.U.; Moore, J.; Behrens-Williams, S.; Panske, A.; Harari, M.; Rokos, H.; Wood, J.M. In vitro and in vivo identification of 'pseudocatalase' activity in Dead Sea water using Fourier transform Raman spectroscopy. J. of Raman Spectroscopy 2002, 33, 586-592. 46. Wynn-Williams, D. D.; Edwards, H. G. M. Proximal analysis of regolith habitats and protective biomolecules in situ by laser Raman spectroscopy: overview of terrestrial Antarctic habitats and Mars analogs. Icarus 2000, 144(2), 486-503. 47. Schopf, J.W.; Kudryavtsev, A.B.; Agresti, D.G.; Wdowiak, T.J.; Czaja, A.D. Laser– Raman imagery of Earth's earliest fossils. Nature 2002, 416(6876), 73-76 48. Marshall, C.P.; Javaux, E.J.; Knoll, A.H.; Walter, M.R. Combined micro-Fourier transform infrared (FTIR) spectroscopy and micro-Raman spectroscopy of Proterozoic acritarchs: a new approach to palaeobiology. Precambrian Rsh 2005, 138(3), 208-224. 49. McKeegan, K.D.; Kudryavtsev, A.B.; Schopf, J.W. Raman and ion microscopic imagery of graphitic inclusions in apatite from older than 3830 Ma Akilia supracrustal rocks, west Greenland. Geology 2007, 35(7), 591-594. 50. Marshall, C.P.; Marshall, A.O. The potential of Raman spectroscopy for the analysis of diagenetically transformed carotenoids. Phil. Trans. of the R. Soc. A 2010, 368(1922), 3137-3144.

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51. Marshall, C.P.; Edwards, H.G.; Jehlicka, J. Understanding the application of Raman spectroscopy to the detection of traces of life. Astrobiology 2010, 10(2), 229-243. 52. Williford, K. H.; Ushikubo, T.; Schopf, J. W.; Lepot, K.; Kitajima, K.; Valley, J. W. Preservation and detection of microstructural and taxonomic correlations in the carbon isotopic compositions of individual Precambrian microfossils. Geochim. et Cosmochim. Acta 2013, 104, 165-182. 53. Sforna, M.C.; van Zuilen, M.A.; Philippot, P. Structural characterization by Raman hyperspectral mapping of organic carbon in the 3.46 billion-year-old Apex chert, Western Australia. Geochim. et Cosmochim. Acta 2014, 124, 18-33. 54. Marshall, C.P.; Marshall, A.O. Raman spectroscopy as a screening tool for ancient life detection on Mars. Phil. Trans. of the R. Soc. A 2014, 372. 55. Bost, N.; Ramboz, C.; LeBreton, N.; Foucher, F.; Lopez-Reyes, G.; De Angelis, S.; Josset, M.; Venegas, G.; Sanz-Arranz, A.; Rull, F.; Medina, J.; Josset, J.L.; Souchon, A.; Ammannito, E.; De Sanctis, M.C.; Di Iorio, T.; Carli, C.; Vago, J.L.; Westall, F. Testing the ability of the ExoMars 2018 payload to document geological context and potential habitability on Mars. Planet. and Space Sci. 2015, 108, 87-97. 56. Lopez-Reyes, G.; Rull, F.; Venegas, G.; Westall, F.; Foucher, F.; Bost, N.; Sanz, A.; Catala-Espi, A.; Vegas, A.; Hermosilla, I.; Sansano, A.; and Medina, J. Analysis of the scientific capabilities of the ExoMars Raman Laser Spectrometer instrument. European J. of Mineralogy 2013, 25, 721-733.

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57. Beegle, L.; Bhartia, R.; White, M.; Deflores, L.; Abbey, W.; Wu, Y.; Cameron, B.; Moore, J.; Fries, M.; Burton, A.; Edgett, K. S.; Ravine, M. A.; Hug, W.; Reid, R.; Nelson, T.; Clegg, S.; Wiens, R.; Asher, S.; Sobron, P. SHERLOC: Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals. IEEE Aerospace Conference, Big Sky, MT, USA 2015, doi: 10.1109/AERO.2015.7119105 58. Gasda, P.J.; Acosta-Maeda, T.E.; Lucey, P.G.; Misra, A.K.; Sharma, S.K.; Taylor, G.J. Next Generation Laser-Based Standoff Spectroscopy Techniques for Mars Exploration. Applied Spectroscopy 2015, 69, 173-192. 59. Meyer, B.; Ospina, M.; Peter, L. B. Raman spectrometric determination of oxysulfur anions in aqueous systems. Analytica Chimica Acta 1980, 117, 301-311. 60. Murata, K.; Kawakami, K.; Matsunaga, Y.; Yamashita, S. Determination of sulfate in brackish waters by laser Raman spectroscopy. Analytica Chimica Acta 1997, 344, 153157. 61. Mosier-Boss, P. A.; Lieberman, S. H. Detection of anions by normal Raman spectroscopy and surface-enhanced Raman spectroscopy of cationic-coated substrates. Applied Spectroscopy 2003, 57(9), 1129-1137. 62. Azbej, T.; Severs, M. J.; Rusk, B. G.; Bodnar, R. J. In situ quantitative analysis of individual H 2 O–CO 2 fluid inclusions by laser Raman spectroscopy. Chem. Geo. 2007, 237(3), 255-263. 63. Sun, Q.; Qin, C. Raman OH stretching band of water as an internal standard to determine carbonate concentrations. Chem.l Geo. 2011, 283, 274-278.

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64. Wu, J.; Zheng, H. Quantitative measurement of the concentration of sodium carbonate in the system of Na2CO3-H2O by Raman spectroscopy. Chem. Geo. 2010, 273, 267-271. 65. Wopenka, B. and Pasteris, J.D. Raman intensities and detection limits of geochemically relecant gas mixtures for a laser Raman microprobe. Analytical Chemistry, 1987, 59, 2165-2170. 66. Carey, D. M.; Korenowski, G. M. Measurement of the Raman spectrum of liquid water. J. of Chem. Physics 1998, 108(7), 2669-2675.

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ACS Earth and Space Chemistry

SO42-

Intensity (normalized and offset)

Intensity (Normalized and Offset)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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5

Na2SO4 in NaCl brine

A

5

1.0 m

4

3

0.05 m 0.01 m 0.005 m

1

0.001 m 4 UPW water

0

850

B

950

ClO4-

1050

SO42-

4

1150

1250

1350

1450

1550

1650

0.1 m

2

0.05 m

1

0.01 m 0.005 m

0

0.001 m UPW water

1750 850

950

5

Na2SO4 in NaClO4 brine

H2O

1.0 m

4

1050

E

SO42-

ClO4-

1150

1250

0

0.005 m

1

0.001 m

UPW water 1150

1250

H2O

0.01 m

0.001 m 1050

1750

0.05 m

2

0.005 m

950

1650

0.1 m

0.01 m

850

1550

1.0 m

3

0.05 m

1

1450

NaClO4 in Na2SO4 brine

0.1 m 2

1350

0.5 m

0.5 m

3

H2O

1.0 m 0.5 m

0.1 m

2

NaClO4 in NaCl brine

ClO4-

D

4

0.5 m

3

5

H2O

UPW water

0

1350

1450

1550

1650

1750

850

950

1050

1150

1250

1350

1450

1550

1650

1750

SO4

Intensity (Normalized and Offset)

2-

5

Na2SO4in UPW

C

1.0 m

4 3

5

0.5 m

4

0.1 m

3

ClO4

-

F

0.1 m 0.05 m

0.005 m 0.001 m 4 UPW water 850

950

1050

1150

1250

H2O

0.5 m

0.01 m

1

NaClO4 in UPW 1.0 m

0.05 m

2

0

H2O

1350

1450

Raman Shi� (cm-1)

1550

1650

2

0.01 m

1

0.005 m 0.001 m

0 1750 850

UPW water 950

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1150

1250

1350

1450

Raman Shi� (cm-1)

1550

1650

1750

Page 27 of 27

15

y = 33.907x + 0.1518 R² = 0.995

20

y = 34.899x + 0.2502 R² = 0.9922

10

934/1640 Peak Height Ra�o

15

981/1640 Peak Height Ra�o

10

5

0

3.5

0

0.1

0.2

0.3

0.4

0.5

3

2.5

y = 40.23x -0.1204 R² = 0.9473

2

5

0 2.5

0.1

0.2

0.3

0.4

0.5

0.04

0.05

y = 41.216x + 0.1048 R² = 0.9783

2

1.5

1.5

1

1

0.5

0.5 0

0

0.01

0.02

0.03

0.04

0

0.05

Na2SO4 Concentra�on (mol/kg)

C

1.4 1.2

5

y = 2.1239x + 0.017 R² = 0.9916

0.6 0.4 0.2 0.1

0.2

0.3

0.4

0.5

0.4

y = 2.0245x + 0.0455 R² = 0.138

0.2

3

0

0.01

0.02

0.03

0.04

2 1 0 6

0

0.1

NaCl

0.3

0.4

3

y = -5.6327x + 0.4711 R² = 0.0076 0

0.01

0.02

0.03

0.04

NaClO4 Concentra�on (mol/kg) Na2SO4

0.5

4

0

0.05

0.2

5

2

Na2SO4 Concentra�on (mol/kg) Brine Matrix

0.03

y = 1.5048x + 0.3733 R² = 0.0573

1 0

0.02

4

0.8

0

0.01

D

6

1

0

0

NaClO4 Concentra�on (mol/kg)

934/1640 Peak Area Ra�o

981/1640 Peak Area Ra�o

B

25

A

20

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NaClO4

UPW

ACS Paragon Plus Environment

0.05