Study of 3–methyl–1,2,3–butanetricarboxylic acid (MBTCA) degradation using mass spectrometry technique and DFT methods

Abstract

3–Methyl–1,2,3–butanetricarboxylic acid (MBTCA) is an important component of secondary organic aerosol (SOA) acting as a tracer for the chemical aging of biogenic SOA by oxidizing reagents. The physical properties, including the kinetic stability of organic compounds recognized as part of SOA, are not fully understood. The energetic stability of the MBTCA anion was studied using advanced and modified mass spectrometry (MS) techniques, combined with theoretical modeling within density functional theory (DFT). Based on energy–resolved collision–induced dissociation (ER–CID) experiments, an energetic description and a detailed degradation molecular mechanism were presented. Decarboxylation (m/z 159 ion) and dehydration (m/z 185 ion) reaction pathways were identified as the main consecutive reaction/degradation mechanisms. Product/fragment structural identification and theoretical potential energy surfaces for all observed MBTCA (m/z 203) ion transitions were described. The analyses showed a very good correlation between experimental and theoretical results. For dehydration 104 kJ/mol and 107 kJ/mol and for decarboxylation 171 kJ/mol and 180 kJ/mol (energies respectively experimental and theoretical calculations). Our findings provide insights into the energetic conditions under which the MBTCA anion can undergo further fragmentation processes under ionic gas–phase conditions.