Abstract DGP2026-6

Protonation-induced chemical transformations of complex organics in mass spectrometry: implications for icy ocean worlds exploration.

Lucía Hortal Sánchez (1), Maryse Napoleoni (1), Ernesto Brunet (2), Fabian Klenner (3), Thomas R. O’Sullivan (1), Mirandah Ackley (1), Gregoire Danger (4), Bernd Abel (5,6), Nozair Khawaja (1), Frank Postberg (1).

1 Institut für Geologische Wissenschaften, Freie Universität Berlin, Germany; 2 Department of Organic Chemistry, Universidad Autónoma de Madrid, Spain; 3 Department of Earth and Planetary Sciences, University of California, Riverside, USA; 4 Aix Marseille Univ, CNRS, Institut Origines, PIIM, Marseille, France; 5 Institute of Chemical Technology, University Leipzig, Linnéstr. 3/D-04103 Leipzig/Germany; 6 Department Space Chemistry and Technology, J. Heyrovsky Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 2155/3, CZ 182 23, Praha 8, EU - Czech Republic.

Impact ionisation mass spectrometers, such as the Cosmic Dust Analyser (CDA) onboard Cassini and the SUrface Dust Analyzer (SUDA) onboard Europa Clipper, are key instruments to investigate the composition of icy ocean moons. They are capable of detecting organics in ice grains ejected from cryovolcanic processes (e.g. Enceladus’ plume) and micrometeoritic bombardment of the icy surface. Laboratory analogue experiments that replicate ice grain impact ionisation mass spectra are crucial in order to reliably identify chemical features of organics in spacecraft data. The laser-induced liquid beam ion desorption (LILBID) technique allows the accurate simulation of impact ionisation mass spectra at a range of impact velocities, by desorbing ionic and neutral molecules and fragments from a μm-sized liquid beam containing water and dissolved analytes. This work investigates amygdalin (C20H27NO11) and its mass spectral fingerprint with LILBID, aiming to assist in the analysis of organic molecules with impact ionisation mass spectrometry. Upon measurement, amygdalin undergoes protonation-induced chemical transformations (PICTs), enabled by the high laser energy input and proton-rich environment created upon disintegration of the water matrix. The observed reactivity is a distinct phenomenon that can be set apart from other well-characterised processes that analytes can be subject to upon measurement with LILBID and impact ionisation mass spectrometry (e.g. fragmentation). PICTs observed in amygdalin feature its initial nitrile group as well as other functional groups obtained after the first transformation (e.g. carboxylic acid), resulting in multiple reactions products identified by their characteristic molecular ions. Complementary measurements with nuclear magnetic resonance spectroscopy confirmed that reactivity does not occur in solution prior to desorption, and must therefore occur under LILBID measurement. In principle, functional groups similar to nitrile (e.g., amide or ketone) in other compounds could also be subject to PICTs. PICTs may also occur with spaceborne impact ionisation, potentially hindering the identification of organics contained in ice grains. The present work builds towards a better understanding of PICTs and their effect(s) on the detection of organic compounds using impact ionisation mass spectrometry, and has key implications for the interpretation of Cassini’s CDA data and for investigations of the composition of icy ocean moons with upcoming space missions (e.g. Europa Clipper or ESA’s large-class mission to Enceladus).