title: Laser ablation atmospheric pressure photoionization mass spectrometry imaging of phytochemicals from sage leaves.
abstract: BACKGROUND
  Despite fast advances in ambient mass spectrometry imaging (MSI), the study of neutral and nonpolar compounds directly from biological matrices remains challenging. In this contribution, we explore the feasibility of laser ablation atmospheric pressure photoionization (LAAPPI) for MSI of phytochemicals in sage (Salvia officinalis) leaves.
  
  
  METHODS
  Sage leaves were studied by LAAPPI-time-of-flight (TOF)-MSI without any sample preparation. Leaf mass spectra were also recorded with laser ablation electrospray ionization (LAESI) mass spectrometry and the spectra were compared with those obtained by LAAPPI.
  
  
  RESULTS
  Direct probing of the plant tissue by LAAPPI efficiently produced ions from plant metabolites, including neutral and nonpolar terpenes that do not have polar functional groups, as well as oxygenated terpene derivatives. Monoterpenes and monoterpenoids could also be studied from sage by LAESI, but only LAAPPI was able to detect larger nonpolar compounds, such as sesquiterpenes and triterpenoid derivatives, from the leaf matrix. Alternative MSI methods for nonpolar compounds, such as desorption atmospheric pressure photoionization (DAPPI), do not achieve as good spatial resolution as LAAPPI (<400 µm).
  
  
  CONCLUSIONS
  We show that MSI with LAAPPI is a useful tool for concurrently studying the distribution of polar and nonpolar compounds, such as phytochemicals, directly from complex biological samples, and it can provide information that is not available by other, established methods.
authors.affiliation: Division of Pharmaceutical Chemistry and Technology, Faculty of Pharmacy, P.O. Box 56 (Viikinkaari 5 E), 00014 University of Helsinki, Helsinki, Finland.
authors.forename: Anu
authors.initials: A
authors.lastname: Vaikkinen
authors.forename: Bindesh
authors.initials: B
authors.lastname: Shrestha
authors.forename: Juha
authors.initials: J
authors.lastname: Koivisto
authors.forename: Risto
authors.initials: R
authors.lastname: Kostiainen
authors.forename: Akos
authors.initials: A
authors.lastname: Vertes
authors.forename: Tiina J
authors.initials: TJ
authors.lastname: Kauppila
mesh_terms: D001274:Atmospheric Pressure; D007834:Lasers; D013058:Mass Spectrometry / Q000379:methods*; D057054:Molecular Imaging / Q000379:methods*; D064209:Phytochemicals / Q000032:analysis / Q000737:chemistry*; D018515:Plant Leaves / Q000737:chemistry*; D027543:Salvia officinalis / Q000737:chemistry*
chemical_list: D064209:Phytochemicals