Gas chromatography coupled-to Fourier transform orbitrap mass spectrometer for enantioselective amino acid analyses: Application to pre-cometary organic analog

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 gasses (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 10⁻⁷ M, 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.