High‐mass resolution molecular imaging of organic compounds on the surface of Murchison meteorite

Abstract

High‐resolution mass spectrometry (HRMS) imaging by desorption electrospray ionization (DESI) coupled with Orbitrap MS using methanol (MeOH) spray was performed on a fragment of the Murchison (CM2) meteorite in this study. Homologues of CnH2n–1N2+ (n = 7–9) and CnH2nNO+ (n = 9–14) were detected on the sample surface by the imaging. A high‐performance liquid chromatography (HPLC)/HRMS analysis of MeOH extracts from the sample surface after DESI/HRMS imaging indicated that the CnH2n–1N2+ homologues corresponds to alkylimidazole, and that a few isomers of the CnH2nNO+ homologues present in the sample. The alkylimidazoles and CnH2nNO+ homologues displayed different spatial distributions on the surface of the Murchison fragment, indicating chromatographic separation effects during aqueous alteration. Moreover, the distribution pattern of compounds is also different among homologues. This is probably also resulting from the separation of isomers by similar chromatographic effects, or different synthetic pathways. Alkylimidazoles and the CnH2nNO+ homologues are mainly distributed in the matrix region of the Murchison by mineralogical observations, which is consistent with previous reports. Altered minerals (e.g., Fe‐oxide, Fe‐sulfide, and carbonates) occurred in this region. However, no clear relationship was found between these minerals and the organic compounds detected by DESI/HRMS imaging. Although this result might be due to scale differences between the spatial resolution of DESI/HRMS imaging and the grain size in the matrix of the Murchison, our results would indicate that alkylimidazoles and the CnH2nNO+ homologues in the Murchison fragment were mainly synthesized by different processes from hydrothermal alteration on the parent body.

New Applications of High-Resolution Analytical Methods to Study Trace Organic Compounds in Extraterrestrial Materials

“…This is in contrast with a previous DESI/HRMS study of the Murray meteorite, which found that the alkylimidazole and alkylpyridine compounds occurred in different locations-that is, these two homologous CHN series were not co-located [17]. Furthermore, a previous DESI/HRMS study of the Murchison meteorite found only alkylimidazole compounds, and no alkylpyridine compounds were detected [18].…”

“…Using a spray of electrically charged solvent such as methanol, soluble organic compounds are desorbed and ionized from the sample for introduction to a mass spectrometer, with a typical surface spatial resolution of 50-100 µm. Molecular imaging of the surface of the Murray and Murchison meteorites were performed by DESI/HRMS, and various alkylated CHN homologous compounds were identified [17,18]. These CHN compounds were distributed heterogeneously in the matrices of both meteorites.…”

“…However, the alkylpyridines and alkylimidazoles occurred separately in different locations (i.e., the C n H 2n−5 N compounds and the C n H 2n−2 N 2 compounds were not co-located [17]), suggesting a different source for each CHN compound series or a possible chromatographic effect associated with fluid movement in the meteorite parent body. In a previous study of the Murchison meteorite [18], only the alkylimidazole series was identified.…”

“…Positive mass spectra were taken by full scan over a range of m/z 62-600 with a mass resolution of m/∆m~140,000 at m/z 200. associated with fluid movement in the meteorite parent body. In a previous study of the Murchison meteorite [18], only the alkylimidazole series was identified.…”

“…Positive ions ranging from m/z 70 to 750 were collected in a full scan mode with a mass resolution of approximately 140,000 (m/Δm at m/z = 200). The detailed analytical procedure has been described elsewhere [18].…”