Preliminary results of Sulfur speciation by µ-XANES and STXM in Extraterrestrial Organics
Motoo Ito1, Ryoichi Nakada1, Hiroki Suga2, Takuji Ohigashi3, Yu Kodama4 and Hiroshi Naraoka51
Kochi Institute for Core Sample Research, JAMSTEC, 2Hiroshima University
3
UVSOR Synchrotron, Inst. Mol. Sci., 4Marine Works Japan, 5Kyushu University
Sulfur is one of the major elements in terrestiral and extraterrestrial organics. The elemental compositions of theMurchison IOM (insolble organic matter) are proposed to be C100H70O22N3S7 [1] or C100H48N1.8O12S2 [2]. Because sulfur
shows a wide range in oxidation state (-2 to +6) with both electropositive and electronegative elements, both reduced andoxidized sulfur species have been found in various carbonaceous chondrites [3, 4]. Therefore, understanding of speciation ofsulfur and its distribution within organics in a carbonaceous chondrite is crucial to provide the secondary alteration processesof thermal metamorphism and aqueous alteration in the parent body.
X-ray absorption near edge spectroscopy (XANES) is a powerful analytical tool to characterize and quantify chemicalspeciation, functional group and bonding environment of the sample. In the field of cosmochemistry, many researches werecarried out to identify functional groups of C, N and O in extraterrestrial organics (i.e., IOM in carbonaceous chondrites [5],cometary returned sample [6], organics found in Hayabusa Category-3 grains [7], organics in IDPs [8]). However, sulfur
study with XANES in the extraterrestrial organics is very rare [3, 9].
In this study, we report preliminary results of sulfur speciation measurements by K- and L3-edge XANES of the IOM
extracted from Asuka 881458 CM2 carbonaceous chondrite. We carried out X-ray fluorescence (XRF) mapping for S and Nwith a spatial resolution of 20 µm in the IOM (0.8 x 1 mm2) at BL27SU of SPring-8. We, then, conducted µ-XAFS (sulfurK-edge) measurements to acquire point spectra (#1-#6 in Fig. 1). In addition, we have measured carbon K-edge and sulfur
L3-edge XANES spectra in the FIB section of the AA881459 IOM (8 x 20 µm2) using scanning transmission X-ray microscope(STXM) at Inst. Mole Sci. UVSOR
42 8   45 2
18 .
82 4. 18 5 Figure 2. Possible sulfur components in the extractedorganics from A881458 obtained by K?edge spectrum.  
.
84BL4U.
Spot1#• 0.8"x"1"mm
Low
High
Spot2#
Figure 1 shows S and N• 37"x"51"pixels"(20"µm/pixel)
Spot3#
Spot4#
S&XRF"image
N&XRF"image
S
Spot5#XRF images together with optical
Optical"microscope"Image
Spot6##6#6
microscope image of the sample on#1#1
the Si wafer. The distributions of#5
#5
S and N are similar but slightly#2 #3 #4
#2 #3 #4
different abundances. We used
these images to determine XANES
1"mmanalysis spots in the sample (about20 µm in size, #1 to #6 in Figure 1).
Measured S K-edge XANES spectra (#1 to #6) have deconvoluted with a least- Figure'3.'Sulfur'L.edge'STXM'image'and'SIM'image'square linear combination best fits to reference spectra of S contained organic and Low&High&FIB section image
inorganic compounds. Figure 2 shows a radar diagram of possible S components
and their abundances in each spot (#1-#6). Each spot has different sulfur containedorganics and inorganics and their abundances. This suggested that extraterrestrialorganics is a complex mixture of several types of sulfur species. Our result is
consistent with previous works [3, 9]. S L3-edge XANES spectra of several Scontained organics with different species (lauryl sulfate, sodium methanesulfonate,
9 µm
L-cysteic acid and DL-methionine sulfone) were obtained as references. Figure 3 S"STXM&image&shows high-resolution (50 nm) S L3-edge STXM image of the FIB section of theAA881459 IOM. It is noted that S is homogeneously distribute and tiny S hot spots were observed within the sample.
However, it is difficult to deconvolute the L3-edge spectra of the sample based on fitting by a linear combination of standard
materials spectra because of lack of the S L3-edge spectra for reference materials at this moment.
2

4!aminothiophenol#
Trimethylsulfonium# 15#
4!nitrobenzen#
Thianthrene#
Anthraquinone#

Sulfoxide#

Sulfonate#

13#
11#

Aroma9c!SH1#

CysAlaAla#9#

pyrrho9te#

Cys9ne#7#5#pyrite#Dibenzothiophene#

3#

Polyphenylenesulﬁde#Dibenzyl#disulﬁde#

1#

!1#

PhCH2SPh#

Dibenzyl#sulﬁde#Octoclothepin#

Dihydrodibenzothiopin#

Na9ve!S#Na2SO4#

Na2SO3#DL!Methionine#
Methylsulfonium#
Methionine#
Methanesulfonic#acid#

DL!methionine#sulfone#

Dothiepin#

gypsum#

HOPhSPhOH#
Lauryl#sulfate#
L!cysteic#acid#

References: [1] Remusat, 2011. EPJ Web of Conferences 18:05002. [2] Gilmour, 2005. In Meteorites, comets and planets,
Treatise on Geochemistry, p.269. [3] Orthous-Daunay et al. 2010. EPSL, 300, 321−328. [4] Cooper et al. 1997. Science, 277,1072−1074. [5] Cody et al. 2011. Meteor Planet Sci 43:353–365. [6] Sanford et al. 2006. Science, 314:1720–1724. [7] Yabuta
et al. 2014. EPS, 66, 156. [8] Flynn et al. 2003. Geochim Cosmochim Acta, 67, 4791–4806. [9] Bose et al. (2017) MeteorPlanet Sci, 52, 546−559.