2021 journal article

Investigations of beta-carotene radical cation formation in infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI)

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, 35(16).

By: M. Bagley n & D. Muddiman n

co-author countries: United States of America 🇺🇸
MeSH headings : Cations / analysis; Cations / chemistry; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / methods; Tandem Mass Spectrometry; beta Carotene / analysis; beta Carotene / chemistry
Source: Web Of Science
Added: July 26, 2021

Radical cationization of endogenous hydrocarbons in cherry tomatoes was previously reported using infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI), a mass spectrometry imaging technique that operates at ambient conditions and requires no sample derivatization. Due to the surprising nature of this odd-electron ionization, subsequent experiments were performed on β-carotene to determine the amount of radical cationization across different sampling conditions.β-Carotene was analyzed across a variety of sample states using IR-MALDESI followed by Orbitrap mass spectrometric analysis: first, as a standard in ethanol in a well plate; second, as particulates on printer paper; and third, as particulates covered by an ice matrix. These techniques were also performed with a β-carotene standard either in solution with a reducing agent (ascorbic acid) or with ascorbic acid in the electrospray solution.Tandem mass spectrometry confirmed the presence of the radical cation of β-carotene by comparing fragments against NIST and METLIN databases. It was always analyzed as a radical cation when sampled from solution, where ascorbic acid increased radical cation abundance when in solution with β-carotene. Mixed-mode ionization between radical cationization and proton adduction was observed from dried particulates using IR-MALDESI.There are several potential mechanisms for β-carotene radical cationization prior to IR-MALDESI analysis, with multiphoton ionization, thermal degradation, and/or reaction with oxygen appearing to be the most logical explanations. Furthermore, although not the primary cause, changing certain aspects of sample conditions can result in significant mixed-mode ionization with competing protonation.