Structural study of analogues of Titan s haze by trapped ion mobility coupled with a Fourier transform ion cyclotron mass spectrometer

TL;DR

This study employs trapped ion mobility spectrometry coupled with ultra-high resolution mass spectrometry to analyze Titan haze analogs, revealing complex molecular structures and isomeric diversity in tholins with advanced visualization techniques.

Contribution

First application of TIMS-FTICR MS to Titan haze analogs, providing detailed structural insights into complex tholin mixtures.

Findings

Identification of CHN5-6 dominant components

Visualization of homolog series and molecular trends

Observation of isomeric diversity variation with m/z

Abstract

The aerosols present in the atmosphere of the Saturn s moon Titan are of particular planetary science interest and several spacecraft missions already allowed to gather spectroscopic data. Titan haze s analogs, so-called tholins, were produced on earth to push forward the comprehension of their formation and properties. In this study, this highly complex mixture was analyzed here for the first time by trapped ion mobility spectrometry coupled to ultra-high resolution mass spectrometry (FTICR MS). Electrospray ionization revealed the characteristic CHNx-class components, with CHN5-6 and DBE 6-7 most abundant. Deploying specialized visualization, enabled by accurate mass measurements and elemental composition assignments, the adapted Kendrick mass defect analysis highlights the C2H3N homolog series, whereas the nitrogen-modified van Krevelen diagram exhibits a clear trend towards H/C 1.5 and N/C 0.5. More interestingly, the representation of m/z versus collision cross section (CCS) allowed hypothesizing a ramified N-PAH structural motif. State-of-the-art IMS is currently not able to resolve the isomeric continuum of ultra-complex mixtures; thus peak parameter other than the CCS-value are explored. As such, analyzing the mobility peak width versus m/z shows a linear increase in isomeric diversity between m/z 170 and 350 and a near plateau in diversity at higher m/z for the N-PAH-like structure. Due to the high complexity of the sample, these structural insights are only to be revealed by TIMS-FTICR MS.