Method Development for the Analysis of Carbonaceous Chondrites by Laser Desorption/Ionization and Secondary Ion Time‐of‐Flight Mass Spectrometry

Abstract

This study focuses on the development of a laser desorption/ionization mass spectrometric method for analyzing carbonaceous chondrites, meteorites that may hold clues to the origin of life. Since carbonaceous chondrites are only available in small quantities, we initially designed an artificial meteorite material (the mineral forsterite) doped with an organic material system (the amino acid tryptophan, the sugar 2-deoxy-D-ribose, and the polycyclic aromatic hydrocarbon triphenylene) as meteorite-like material to develop an LDI-MS method. This simulates a simplified artificial meteoritic composition to study the behavior of organic compounds in an inorganic environment. Experiments with meteorite-like material were performed on four different LDI-MS instruments (reflectron TOF-MS and QTOF-MS) with different performance characteristics (e.g., different lasers and laser repetition rates, different ion source pressure) in positive- and negative-ion mode and compared the data with those obtained on a TOF-SIMS instrument. Real meteoritic samples were also analyzed using our previously developed LDI-MS method and the TOF-SIMS method. For sample preparation, we used an in-house built micro-press, enabling the fixing of both meteorite-like material and real meteoritic splinters onto a target plate. Our unique target system, a universal in-house-designed adapter target holder, facilitated compatibility with all instruments including SIMS from different manufacturers. In the real meteorite samples a variety of elements, including potential detections of rubidium (⁸⁵Rb:⁸⁷Rb = 3:1), cesium (¹³³Cs only), and tentatively holmium (¹⁶⁵Ho only) was predominantly detected in positive-ion mode. Utilizing LDI with a reflectron TOF-MS in negative-ion mode, we identified distinct carbon clusters ranging from C<inf>2</inf> to C<inf>13</inf> in the Allende and Jbilet Winselwan meteorites originating most likely from high molecular weight organic carbon compounds. Background analysis confirmed a minimal impact of external contamination with carbon cluster ions validating the authenticity of these findings. No distinct other carbon-containing material could be identified.