Identify low mass volatile organic compounds from cometary ice analogs using gas chromatography coupled to an Orbitrap mass spectrometer associated to electron and chemical ionizations

Abstract

Analysis of organic matter extracted from meteorites showed that solar system objects present an important molecular diversity. To improve our understanding of such organic matter, new analytical technologies must be developed. The present study displays the first experiments using a GC-FT-Orbitrap-MS to decipher the molecular diversity observed in experiments simulating the evolution of cometary ices. The proposed analytical strategy focuses on the analysis of 110 volatile organic compounds (VOC) with mainly 1 to 6 carbon atoms generated in such cometary ice analogs. Electron ionization (EI) and chemical ionization (CI) modes with methane (CH4) or ammonia (NH3) were optimized and compared. Those developments maximized the intensity of molecular, protonated or deprotonated ions, and improved high-resolution molecular formula unambiguous identification: EI mode is too energetic to provides there detection, while it is not the case in CI mode. Particularly, NH3 as a reagent gas improves amine identification in positive mode (PCI), and esters, alcohols, carbonyls, amides, carboxylic acids and nitriles in negative mode (NCI). The combination of both EI and CI mass spectrum analysis improves molecular identification, thanks to the detection of molecular, deprotonated or protonated ion of highest intensity and fragment formula assignments. The EI and NCI NH3 combination allows formula assignments up to 94% of our database with limit of detection up to 7 ppm. This procedure has been validated for untargeted GC-FT-Orbitrap-MS analysis of VOC coming from the processing of cometary ice analogs.