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Formation of the exceptional [M − H] + cation in atmospheric pressure ionization mass spectrometry analysis of 2‐(diphenylsilyl) cyclopropanecarboxylate esters
Author(s) -
Wang Ruoqian,
Zhao Zhiyuan,
Zhang Huarong,
Sheng Chunqi,
Wang Yan,
Jiang Kezhi
Publication year - 2020
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.8866
Subject(s) - chemistry , mass spectrometry , ion , electrospray ionization , ionization , protonation , molecule , ion source , atmospheric pressure chemical ionization , solvent , analytical chemistry (journal) , chemical ionization , density functional theory , atmospheric pressure , polyatomic ion , computational chemistry , chromatography , organic chemistry , oceanography , geology
Rationale In general, ionization of analytes in atmospheric pressure ionization mass spectrometry (API‐MS) in positive ion mode results in the formation of protonated molecules ([M + H] + ) and/or cationized molecules (e.g., [M + Na] + ). The formation of specific [M − H] + cations in the API process is of significant interest for further investigation. Methods The ionization processes of 2‐(diphenylsilyl)‐1‐phenyl‐cyclopropanecarboxylate esters were investigated using electrospray ionization (ESI)‐MS and atmospheric pressure chemical ionization–MS in positive ion mode. Theoretical calculations were carried out with the Gaussian 03 program using the density functional theory (DFT) method at the B3LYP/6‐311 + G(2d,p) level. Results The anomalous [M − H] + ion and the regular [M + Na] + ion were both observed using ESI–MS. Interestingly, no [M + H] + ion was obtained in the ESI–MS analysis, and acidification of the ESI solvent accelerated the formation of [M − H] + rather than [M + H] + ion. DFT calculations for the typical methyl 2‐(diphenylsilyl)‐1‐phenyl‐cyclopropanecarboxylate ( 1 ) indicated that the [ 1 + H] + ion can thermodynamically and kinetically undergo facile H 2 elimination to generate [ 1 − H] + . Conclusions The favorable formation of [M − H] + ions in these compounds is attributed to the unique diphenylhydrosilyl group in their structure. The [M + H] + ion formed easily underwent H 2 elimination to produce the [ 1 − H] + ion in the API source, and thus, acidification of the ESI solvent apparently accelerates the formation of the [ 1 − H] + ion.