title: Differentiation of prototropic ions in regioisomeric caffeoyl quinic acids by electrospray ion mobility mass spectrometry.
abstract: BACKGROUND
  A series of dietary important regioisomeric chlorogenic acids were investigated by ion mobility mass spectrometry (IM-MS). The existence of prototropic isomers separated in the drift dimension was observed and investigated further using tandem mass spectrometry (MS/MS) and compared with suitable synthetic analogues.
  
  
  METHODS
  Using a quadrupole ion mobility time-of-flight mass spectrometer, the IM-MS and IM-MS/MS spectra of selected chlorogenic acids were recorded in the negative ion mode and compared with synthetic analogues.
  
  
  RESULTS
  Regioisomeric di- and monocaffeoyl quinic acids can be readily separated and investigated using IM-MS. Comparison of drift times allows assignment of the regiochemistry of precursor ions as well as for fragment ions. For 5-caffeoyl quinic acid the existence of prototropic ions was suggested and probed using synthetic analogues, unable to show this type of isomerism. These investigations suggest the presence of prototropic isomers with carboxylate and phenolate sites, respectively.
  
  
  CONCLUSIONS
  We report on IM-MS measurements on regioisomeric mono- and dicaffeoyl quinic acids, which are important dietary natural products. Both classes of compounds can be readily separated by IM-MS in the drift time dimension and, following MS(2) experiments, fragment ion regiochemistry unambiguously determined. 5-Caffeoyl quinic acid shows two IM-MS signals, which we assign to prototropic isomers after comparison with suitable synthetic analogues, with a negative charge located at the carboxalate or phenolate functionality, respectively.
authors.affiliation: School of Engineering and Science, Jacobs University Bremen, Campusring 8, 28759, Bremen, Germany.
authors.forename: Nikolai
authors.initials: N
authors.lastname: Kuhnert
authors.affiliation: School of Engineering and Science, Jacobs University Bremen, Campusring 8, 28759, Bremen, Germany.
authors.forename: Ghada H
authors.initials: GH
authors.lastname: Yassin
authors.affiliation: School of Engineering and Science, Jacobs University Bremen, Campusring 8, 28759, Bremen, Germany.
authors.forename: Rakesh
authors.initials: R
authors.lastname: Jaiswal
authors.affiliation: School of Engineering and Science, Jacobs University Bremen, Campusring 8, 28759, Bremen, Germany.
authors.forename: Marius F
authors.initials: MF
authors.lastname: Matei
authors.affiliation: Unilever R&D, Olivier van Noortlaan 120, 3133 AT, Vlaardingen, The Netherlands.
authors.forename: Christian H
authors.initials: CH
authors.lastname: Grün
mesh_terms: D002109:Caffeic Acids / Q000032:analysis* / Q000737:chemistry*; D007477:Ions / Q000032:analysis / Q000737:chemistry; D007536:Isomerism; D011801:Quinic Acid / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods
chemical_list: D002109:Caffeic Acids; D007477:Ions; C472707:caffeoylquinic acid; D011801:Quinic Acid