title: Effects of a proton-conducting ionic liquid on secondary ion formation in time-of-flight secondary ion mass spectrometry.
abstract: BACKGROUND
  A protic ionic liquid, diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]), has low vapor pressure and high protonic conductivity even at room temperature. Since [dema][TfO] has a mobile proton in its salt structure, its primary beam is expected to enhance the formation of protonated molecular ions. However, mass spectrometric characteristics of [dema][TfO] are not well known. In order to develop an ionic-liquid primary beam source, it is necessary to investigate such characteristics.
  
  
  METHODS
  The first time-of-flight secondary ion mass spectrometry (TOF-SIMS) experiment using an Ar(+) primary ion beam was performed to analyze two samples: a neat [dema][TfO] sample and a mixed sample of arginine and [dema][TfO]. Beam characteristics of [dema][TfO] generated by vacuum electrospray were investigated using an apparatus for measuring transient responses of a beam current. The second TOF-SIMS experiment using a [dema][TfO] primary beam was performed to analyze three samples: arginine, a mixture of arginine and [dema][TfO], and poly(ethylene glycol) (PEG300).
  
  
  RESULTS
  The [dema][TfO] primary beam was useful in generating protonated arginine; however, it was not helpful in detecting PEG300. The results were explained by considering gas-phase basicities and proton affinities of analytes and [dema][TfO] constituents. Projectile energy per nucleon of the [dema][TfO] beam was examined; it would be necessary to reduce m/z values of ionic-liquid charged droplets. In addition, a screening method was proposed to select ionic liquids suitable for primary ion beams.
  
  
  CONCLUSIONS
  Since [dema][TfO] can act as a proton source, its primary beam can effectively generate protonated secondary ions of analytes. Consequently, proton-conducting ionic liquids such as [dema][TfO] are expected to have great potentials as primary ion beams in TOF-SIMS.
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba-shi, Ibaraki-ken, 305-8568, Japan.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Fujiwara
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba-shi, Ibaraki-ken, 305-8568, Japan.
authors.forename: Naoaki
authors.initials: N
authors.lastname: Saito