Available online 3 June 2023, 464118

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Gas chromatography (GC) is a separation technique commonly developed for targeted in situ analyses in planetary space missions. It is coupled with low-resolution mass spectrometry to obtain additional structural information and allow compound identification. However, ground-based analyses of extraterrestrial samples have shown the presence of large molecular diversities. For future targeted in situ analyses, it is therefore essential to develop new technologies. High resolution mass spectrometry (HRMS) is currently being spatialized using FT-orbitrap-MS technology. In this contribution, the coupling of gas chromatography with FT-orbitrap-MS is studied for targeted amino acid analyses. The method for enantioselective separation of amino acids was optimized on a standard mixture comprising 47 amino acid enantiomers. Different ionization modes were optimized, chemical ionization with three different reactive gases (NH3, CH4 and NH3/CH4) and electron impact ionization at different electron energies. Single ion and full scan monitoring modes were compared, and detection and quantification limits were estimated by internal calibration under the optimized conditions. The GC-FT-orbitrap-MS demonstrated its ability to separate 47 amino acid enantiomers with minimal co-elution. Furthermore, due to the high mass resolution and accuracy of FT-orbitrap-MS, with mass extraction, the S/N is close to zero, allowing average LOD values of 10⁻7M, orders of magnitude lower than conventional GC-MS techniques. Finally, these conditions were tested for enantioselective analysis of amino acids on an analog of a pre-cometary organic material showing similarities to that of extraterrestrial materials.

Section snippetsINTRODUCTION

The understanding of the origin of the solar system is partly linked to the characterization of the organic content of comets or asteroids. These interplanetary bodies are indeed considered to have evolved little since the formation of the solar system and thus possess a primitive organic content [1], [2], [3]. To characterize this organic matter, ground-based or space observations are possible, but are limited to the identification of molecules either in the gas phase [4], [5], [6] or to the

Chemicals and solutions

For amino acid analyses, each amino acid was prepared individually and then mixed together in 0.1 M hydrochloric acid (HCl) (required for adequate derivatization yiels) to obtain a stock solution of 10⁻4 M (Table 1). Serial dilutions were prepared for calibration curves. The 0.1 M HCl solution was prepared by diluting 6 M HCl (for amino acid analysis ampoule, Merck) in ultra-pure water produced by a Direct-Q® 3 UV water purification system. All amino acids and chemicals used were from

Chromatographic separation, high resolution, and mass accuracy

The implemented chromatographic method allowed for resolving almost all forty-seven amino acids (Figure 1, and Table 2), with only three coelutions being observed. Co-elution concerns l-norleucine/l-β-leucine, d-methionine/d-glutamic acid, and l-methionine/l-glutamic acid. However, because of the high resolution of the mass spectrometer, it is possible to discern these co-eluting analytes (Table 2). The high mass accuracy provided by the Orbitrap technology allows for the unambiguous

Application of optimized conditions to the detection of amino acids in a pre-cometary analog

A pre-cometary analog was formed at low temperature (77 K) and pressure (10⁻7 mbar) from an ice analog containing H2O:13CH3OH:NH3 in ratio 3:1:1 irradiated at 121 nm during 72 h. The photo-processed ice was then heated up to 300 K to obtain an organic residue, which is considered as an analog to pre-cometary material. The resulting organic residue was hydrolyzed during 24 h at 100°C in 6N HCl, and amino acids were searched for in the resulting sample. The analysis of the residue was carried out

CONCLUSION

In this contribution, we investigated the interest of coupling gas chromatography to high-resolution mass spectrometry, a FT-Orbitrap-MS, presenting a resolution of 60 000 at m/z 200. This system was tested for the characterization of derivatized amino acids in a laboratory produced sample analog to pre-cometary organic matter. Ionization modes were first tested and optimized. The molecular ion was only obtained with enough intensities in the positive chemical ionization mode with NH3 or CH4/NH3

CRediT authorship contribution statement

A. Garcia: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Writing – original draft, Visualization. C. Serra: Investigation, Writing – review & editing. Q. Blancart Remaury: Investigation. A.D. Garcia: Investigation. M. Righezza: Formal analysis, Writing – review & editing. C. Meinert: Resources, Writing – review & editing. P. Poinot: Resources, Writing – review & editing. G. Danger: Resources, Writing – original draft, Writing – review & editing,

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The research was funded by the Centre National d'Etudes Spatiales (CNES, R-S18/SU-0003-072 and R-S18/SU-0003-072, PI: G. D.), and the Centre National de la Recherche Française (CNRS) with the programs “Physique et Chimie du Milieu Interstellaire” (PCMI-PI:G.D.) and “Programme National de Planétologie” (PNP) (PI: G.D.). G.D is grateful to the Agence Nationale de la Recherche for funding via the ANR RAHIIA_SSOM (ANR-16-CE29-0015) and VAHIIA (ANR-12-JS08-0001). The project has further received

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