Organics in the Murchison Meteorite Using Carbon XANES Spectroscopy

Introduction: The Murchison meteorite is a carbonaceous chondrite recovered in Australia in 1969. There have been a number of studies reporting organics in this meteorite ranging from simple amino acids [1], aldehydes and ketones [2], sugars [3], carboxylic acids [4] and aromatic hydrocarbons [5]. The techniques involved in these analyses require a substantial amount of work and in some cases the mixing of the meteoritic organic with other organic compounds in either an extraction process or in the analytical procedure. We report here a very simple technique to characterize the organics in the Murchison meteorite. Technique: Several small pieces, approximately 800 microns in size, of the Murchison meteorite were crushed between two, clean, glass slides. The part of the meteorite that remained on the glass slide after tapping was suspended in 600 μl of sterilized water ( Sigma no. W3500). A copper TEM grid, backed with silicon monoxide was used to collect material from the surface and near surface of the water droplet. Any soluble material formed a thin film on the gird substrate and the rest of the particles were randomly distributed over the whole of the TEM grid. This technique selects for particles less then ~3 microns in size with most of the particles in the sub-micron size range. It biases against large crystals, which our prior analyses show to contain little or no detectable organic matter. Thus, we concentrate the organic matter in a process that subjects the sample only to gentle crushing and water. The Scanning Transmission X-ray Microscope [STXM] located at beamline X1A1 at the National Synchrotron Light Source was used to collect absorption images and carbon X-Ray Absorption Near Edge Structure [XANES] spectroscopy [6 ]. Results.: Spectra collected fell into 3 major categories; water soluble organics, water insoluble organics and water insoluble inorganic carbon. Only a representative group of spectra are reported here. Figure 1 shows three spectra from the water soluble organic group in the Murchison meteorite and three standard spectra that exhibit similar features. The first spectrum (a.) is also similar to spectra we have seen in the Tagish Lake meteorite [7]; the standard spectra (b.) that plots nearly exactly to this spectrum is from a phospholipid. The second spectrum (c.) in figure 1. resembles that of a monosaccharide, the standard spectrum (d.) is from glucose. Sugars have been reported in Murchison by others [3]. The third spectrum (e.) is similar to bacterial protein. We have also seen this in the Tagish Lake meteorite. The standard spectrum (f.) is from Bacillus subtilis. Figure 2 shows three spectra of water-insoluble material from Murchison. Spectrum (b.) is that of organic-rich acid insoluble residue from Murchison, not from the crushed meteorite. The other 2 spectra (a. and c.) are from the crushed sample.