Loss of H2 and CO from Protonated Aldehydes in Electrospray Ionization Mass Spectrometry

Published

September 15, 2014

Author(s)

Pedatsur Neta, Yamil Simon, Yuxue Liang, Stephen Stein

Abstract

Electrospray ionization mass spectrometry of 3-formylchromones and 3-formylcoumarins shows that collision-induced dissociation of the protonated ions results in elimination of H¬¬2 as a major fragmentation route. This loss of H2 yields an unstable carbonyl cation, which is susceptible to rapid reaction with water to form a protonated carboxylic acid. This process can take place in the electrospray source and in the collision cell. Consequently, the fragment ions observed in the MS/MS spectrum include those derived from the aldehyde and from the corresponding carboxylic acid. Elimination of CO from the original protonated ions is observed as a minor route in these aldehydes, while other aldehydes exhibit loss of CO and little loss of H2. Studies reveal that aldehydes which protonate predominantly on their carbonyl group or contain a remote basic site for stable protonation, such as a pyridine ring, undergo loss of CO. But aldehydes which contain a vicinal group that forms a hydrogen bridge with a protonated formyl group undergo significant loss of H2, which leads effectively to oxidation and to more complex MS/MS spectra. In the chromone and coumarin derivatives, this complication arises when the formyl group is located on a ring position adjacent to the oxo group. DFT calculations show that elimination of H2 from the protonated aldehyde leaves behind a relatively stable acylium ion, better described as a ketene cation. Hydration of this cation can lead to more complex MS/MS spectra, which may distort MRM results and lead to erroneous identification in library search results.

Citation

Rapid Communications in Mass Spectrometry

Volume

28

Pub Type

Journals

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Keywords

Aldehydes, collision-induced dissociation, fragmentation, tandem mass spectrometry, formylchromones, formylcoumarins, H2 elimination

Citation

Neta, P. , Simon, Y. , Liang, Y. and Stein, S. (2014), Loss of H2 and CO from Protonated Aldehydes in Electrospray Ionization Mass Spectrometry, Rapid Communications in Mass Spectrometry, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=913827 (Accessed April 18, 2024)