# Protonation-Induced Chemical Transformations in Mass Spectrometry: Implications for Detecting Complex Organics on Icy Moons

## TL;DR

This study explores how protonation during mass spectrometry can alter complex organic molecules like amygdalin, which has implications for analyzing organic compounds on icy moons.

## Contribution

The paper reveals a new type of reactivity in amygdalin during LILBID measurements due to protonation-induced chemical transformations.

## Key findings

- Amygdalin undergoes unexpected chemical transformations during LILBID due to protonation.
- These transformations are distinct from typical fragmentation and occur during measurement, not in solution.
- Similar compounds with nitrile, amide, or ketone groups may also experience protonation-induced reactivity.

## Abstract

Impact ionization mass spectrometers, such as Cassini’s
Cosmic Dust Analyzer, are capable of detecting macromolecular organic
compounds in ice grains ejected from icy moons such as Enceladus and
Europa. The identification of their chemical features relies on laboratory
analogue experiments that replicate ice grain impact ionization mass
spectra, such as the laser-induced liquid beam ion desorption (LILBID)
technique. Both space-borne instruments and analogue experiments require
a deeper understanding of measurement-associated processes affecting
mass spectral features, and in particular protonation-induced chemical
transformations (PICTs). Here, we investigate the molecule amygdalin
(C20H27NO11) as a model high-mass,
complex organic compound using LILBID to determine its mass spectral
fingerprint. Our results show that amygdalin undergoes unexpected
PICTs enabled by the high laser energy input upon measurement. The
chemical transformations are promoted by the proton-rich environment
created upon the disintegration of the water matrix. This reactivity
is distinct from other well-characterized phenomena affecting analytes
under LILBID conditions (e.g., fragmentation). Protonation triggers
reactivity in amygdalin’s nitrile group resulting in multiple
products that appear as characteristic molecular ions. Nuclear magnetic
resonance spectroscopy experiments confirm that this reactivity occurs
under LILBID measurement, not in solution prior to desorption. Compounds
with similar functional groups (e.g., amide or ketone) could, in principle,
also be subject to PICTs. PICTs could also occur in space during space-borne
impact ionization, potentially complicating the identification of
analytes embedded in ice grains. Our work builds toward a better understanding
of the effects of PICTs in the detection of organic compounds with
impact ionization mass spectrometry.