Amino acid compositions in heated carbonaceous chondrites and their compound-specific nitrogen isotopic ratios

Q. H. S. Chan1,2,*, Y. Chikaraishi1, Y. Takano1, N. O. Ogawa1, and N. Ohkouchi1

1Department of Biogeochemistry, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima, Yokosuka, Kanagawa 237-0061, Japan

2Present address: NASA Johnson Space Center, 2101 NASA Parkway, Houston, Texas 77058, USA.

*Corresponding author: Q. H. S. Chan. E-mail address: . Tel: +1 (281) 483-4143. Fax: +1 (281) 483-5347

Supplementary Figure and Legend

Figure S1

GC/C/IRMS chromatogram of the 12 M HCl-hydrolyzed hot-water extracts of the Piv/iPr amino acid esters in Y-980115. The subgraph (a) shows the magnified region with the alanine and glycine peaks. The single-ion traces GC/MS chromatograms of (b) Y-980115 and (c) amino acid standard mixture of the same region as shown in (a) indicate that no coeluting compounds were present that could have interfered the IRMS analysis of Y-980115 and that only alanine and glycine arethe main nitrogen-bearing compounds in the region.

Supplementary text

From both the amino acid standard mixture and Y-980115 chromatograms we can see that no coeluting compounds would interfere the IRMS analysis of Y-980115. Even the potential compound (compound X, marked as red arrow, m/z 130) eluted close to but after alanine, is shown at a much higher abundance as compared to glycine, which is surely not to be confused with the lower abundance alanine as identified in the IRMS chromatogram. These unknown compounds (e.g. compounds X and Y as marked on the GC/MS chromatogram of Y-980115) could have been derived from the gas introduced to the MS of the GC/MS, which was removed from the IRMS system thanks to the combustion/reduction furnaces and liquid nitrogen trap in the system that are installed for removing compounds generated during amino acid combustion (Chikaraishi et al., 2010). Therefore, the gas introduced to the IRMS ion source is much cleaner without any excess compounds but N2, leading to a very high sensitivity achieved in our study. Clearly both the unknown compounds are not nitrogen-bearing compounds and thus they can only be identified in the GC/MS but not the GC/C/IRMS chromatogram. A nitrogen–phosphorus detector (NPD) chromatogram can “witness” these compounds, but on the other hand NPD lacks the MS capability and its sensitivity is not as good as GC/C/IRMS without the furnaces and liquid nitrogen trap. Therefore, the nitrogen isotopic values shown in Figure 3are unambiguously extraterrestrial and indigenous to the meteorite sample.