title: Neutral losses of sodium benzoate and benzoic acid in the fragmentation of the [M + Na]+ions of methoxyfenozide and tebufenozide via intramolecular rearrangement in electrospray ionization tandem mass spectrometry.
abstract: BACKGROUND
  Electrospray ionization (ESI) tandem mass spectrometry can be applied to determine structural information about organic compounds. The [M + Na]+ion is one of the major precursor ions in ESI mass spectrometry, but its fragmentation mechanism study is still insufficient. This study reveals the interesting fragmentation reactions of the [M + Na]+ions of methoxyfenozide and tebufenozide.
  
  
  METHODS
  The fragmentations of the [M + Na]+, [M + Li]+, and [M + H]+ions of methoxyfenozide and tebufenozide were studied using a hybrid quadrupole-orbitrap mass spectrometer and an ion trap mass spectrometer. A hydrogen/deuterium (H/D)-exchange experiment in the amide group of methoxyfenozide allowed for the confirmation of the fragmentation mechanism. Density functional theory (DFT) calculations were performed for a further understanding of the fragmentation mechanism of the [M + Na]+ion of methoxyfenozide.
  
  
  RESULTS
  Neutral losses of sodium benzoate and benzoic acid in the fragmentation of the [M + Na]+ions of methoxyfenozide and tebufenozide were observed as the major fragmentation pathways. In contrast, similar fragmentations were not observed or minor pathways in the fragmentation of the [M + Li]+and [M + H]+ions of methoxyfenozide and tebufenozide. In addition, a minor product ion resulting from loss of NaOH was identified, which was the first reported example in the fragmentation of sodiated compounds in mass spectrometry.
  
  
  CONCLUSIONS
  Losses of sodium benzoate and benzoic acid in the fragmentation of the [M + Na]+ions of methoxyfenozide and tebufenozide are proposed to be formed through an intramolecular rearrangement reaction, which is supported by DFT calculations. An H/D-exchange experiment confirms that the carboxyl hydrogen of benzoic acid and the hydrogen of NaOH exclusively derive from the amide hydrogen of the precursor ion. This study enriches our knowledge on the Na+-induced fragmentation reactions. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: Tea Research Institute, Chinese Academy of Agricultural Sciences, 9 South Meiling Road, Hangzhou, 310008, P.R. China.|Laboratory of Quality & Safety Risk Assessment for Tea (Hangzhou), Ministry of Agriculture, Hangzhou, 310008, P.R. China.
authors.forename: Yunfeng
authors.initials: Y
authors.lastname: Chai
authors.affiliation: Tea Research Institute, Chinese Academy of Agricultural Sciences, 9 South Meiling Road, Hangzhou, 310008, P.R. China.|Laboratory of Quality & Safety Risk Assessment for Tea (Hangzhou), Ministry of Agriculture, Hangzhou, 310008, P.R. China.
authors.forename: Guanwei
authors.initials: G
authors.lastname: Gao
authors.affiliation: Department of Chemistry, Zhejiang University, Hangzhou, 310027, P.R. China.
authors.forename: Shanshan
authors.initials: S
authors.lastname: Shen
authors.affiliation: Tea Research Institute, Chinese Academy of Agricultural Sciences, 9 South Meiling Road, Hangzhou, 310008, P.R. China.|Laboratory of Quality & Safety Risk Assessment for Tea (Hangzhou), Ministry of Agriculture, Hangzhou, 310008, P.R. China.
authors.forename: Xin
authors.initials: X
authors.lastname: Liu
authors.affiliation: Tea Research Institute, Chinese Academy of Agricultural Sciences, 9 South Meiling Road, Hangzhou, 310008, P.R. China.|Laboratory of Quality & Safety Risk Assessment for Tea (Hangzhou), Ministry of Agriculture, Hangzhou, 310008, P.R. China.
authors.forename: Chengyin
authors.initials: C
authors.lastname: Lu