title: Collision-induced dissociation studies of caffeine in positive electrospray ionisation mass spectrometry using six deuterated isotopomers and one N1-ethylated homologue.
abstract: BACKGROUND
  In order to deepen the understanding of electrospray ionisation collision-induced dissociation (ESI-CID) fragmentation reactions of xanthine derivatives for the identification of metabolites using low-resolution liquid chromatography/mass spectrometry (LC/MS) analysis, basic experiments using caffeine (1,3,7-trimethylxanthine) as model compound have been performed.
  
  
  METHODS
  Six deuterium isotopomers and one N1-ethylated homologue of caffeine have been synthesized and their ESI fragmentation spectra have been obtained by using LC/MS in combination with either standard or perdeuterated eluent mixtures.
  
  
  RESULTS
  One result of these studies is the finding that the positive charges of the ESI-CID caffeine fragments are caused by the addition of protons. Furthermore, the performed experiments allow the determination of all molecular formulae of each ESI-CID caffeine fragment.
  
  
  CONCLUSIONS
  As basic CID reactions of caffeine have been elucidated in this work, the developed fragmentation scheme may serve as a valuable tool for the interpretation of ESI-CID fragmentation spectra of more complex xanthine derivatives and their respective metabolites.
authors.affiliation: Institut für Neurowissenschaften und Medizin (INM-5), Forschungszentrum Jülich GmbH, 52425, Jülich, Germany. d.bier@fz-juelich.de
authors.forename: Dirk
authors.initials: D
authors.lastname: Bier
authors.forename: Rudolf
authors.initials: R
authors.lastname: Hartmann
authors.forename: Marcus
authors.initials: M
authors.lastname: Holschbach
mesh_terms: D002110:Caffeine / Q000031:analogs & derivatives* / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D003903:Deuterium / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D007536:Isomerism; D008958:Models, Molecular; D008968:Molecular Conformation; D009587:Nitrogen Isotopes / Q000737:chemistry; D011522:Protons; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D007477:Ions; D009587:Nitrogen Isotopes; D011522:Protons; D002110:Caffeine; D003903:Deuterium