title: Observation of CO2 and solvent adduct ions during negative mode electrospray ionization Fourier transform ion cyclotron resonance mass spectrometric analysis of monohydric alcohols.
abstract: BACKGROUND
  Monohydric alcohols are common in natural products, bio-oils, and medicine. We have found that monohydric alcohols can form O3 (ions containing three oxygen atoms) and O4 adduct ions in negative electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), which would significantly affect the composition analysis of alcohols, especially in a complex mixture. It is necessary to study the reaction pathways and the method to eliminate or reduce the 'artifact' adducts.
  
  
  METHODS
  Octadecanol, cholesterol, squalanol and two complex monohydric alcohol mixtures were selected as model compounds. These samples were subjected to negative ion ESI FT-ICR MS analysis. The composition and formation mechanism of adducts were studied by the ultrahigh-resolution accurate mass measurement for elemental composition, along with the MS(2) isolation and collision-induced dissociation (CID) experiments for structural determination.
  
  
  RESULTS
  The reaction pathway of O3 adduct formation is the coupling of a monohydric alcohol ion with a CO2 to form a stable O3 ionic species by likely a covalent bond (source of CO2 is not clear). The O4 species are formed by O3 ionic species adducted with an alcohol molecule of the solvent, such as methanol or ethanol, by likely a hydrogen bond. These adduct ions could be eliminated or reduced by increasing collision energy. However, excessive collision energy would fragment monohydric alcohol ions.
  
  
  CONCLUSIONS
  The formation mechanisms of O3 and O4 adducts from monohydric alcohols in negative ion ESI FT-ICR MS were proposed. The solvent adduction effects can be eliminated or reduced by optimizing the collision energy of CID in FT-ICR MS.
authors.affiliation: State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, China; College of Pharmacy, Liaoning Medical University, Jinzhou, Liaoning, 121001, China.
authors.forename: Xibin
authors.initials: X
authors.lastname: Zhou
authors.forename: Yahe
authors.initials: Y
authors.lastname: Zhang
authors.forename: Suoqi
authors.initials: S
authors.lastname: Zhao
authors.forename: Chang Samuel
authors.initials: CS
authors.lastname: Hsu
authors.forename: Quan
authors.initials: Q
authors.lastname: Shi
mesh_terms: D000438:Alcohols / Q000737:chemistry*; D002245:Carbon Dioxide / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000295:instrumentation / Q000379:methods
chemical_list: D000438:Alcohols; D007477:Ions; D012997:Solvents; D002245:Carbon Dioxide