title: Transmission mode desorption atmospheric pressure photoionization.
abstract: BACKGROUND
  Desorption atmospheric pressure photoionization (DAPPI) is an ambient mass spectrometry (MS) technique that is suitable for the direct analysis of polar and nonpolar compounds from a variety of surfaces. Conventional DAPPI uses reflection geometry, but here transmission mode (TM)-DAPPI is introduced for fast and easy analysis of liquid samples.
  
  
  METHODS
  Stainless steel and PEEK meshes were used as sampling support in TM-DAPPI. The sample was applied either in the form of a droplet on the mesh, or by dipping the mesh in the sample solution. Physical parameters affecting the ionization efficiency were optimized for TM-DAPPI. The mesh materials were used to extract compounds from aqueous samples, which were then analyzed by TM-DAPPI. TM-DAPPI and conventional DAPPI were compared.
  
  
  RESULTS
  In TM-DAPPI, intense signals for the analytes were achieved with less heating power, and lower nebulizer gas and dopant flow rates than optimally used in conventional DAPPI. Either due to this, or the different sample support material used, a much lower background and improved sensitivity compared to conventional DAPPI was achieved. The analytes could be extracted and concentrated from liquid samples on the mesh material used in TM-DAPPI, which was especially efficient for the nonpolar benzo[a]pyrene. This effect was utilized in the analysis of triacylglycerols from cow milk.
  
  
  CONCLUSIONS
  While conventional DAPPI is still the method of choice for solid samples, TM-DAPPI can be utilized as a fast, easily automated method for analyzing liquid samples. The mesh materials can be utilized for extraction of low polarity compounds, such as steroid hormones or PAHs from dilute, aqueous solutions, followed by subsequent analysis by TM-DAPPI.
authors.affiliation: Faculty of Pharmacy, University of Helsinki, P.O. Box 56, 00014, University of Helsinki, Finland.
authors.forename: Anu
authors.initials: A
authors.lastname: Vaikkinen
authors.affiliation: Faculty of Pharmacy, University of Helsinki, P.O. Box 56, 00014, University of Helsinki, Finland.
authors.forename: Juha
authors.initials: J
authors.lastname: Hannula
authors.affiliation: Faculty of Pharmacy, University of Helsinki, P.O. Box 56, 00014, University of Helsinki, Finland.
authors.forename: Iiro
authors.initials: I
authors.lastname: Kiiski
authors.affiliation: Faculty of Pharmacy, University of Helsinki, P.O. Box 56, 00014, University of Helsinki, Finland.
authors.forename: Risto
authors.initials: R
authors.lastname: Kostiainen
authors.affiliation: Faculty of Pharmacy, University of Helsinki, P.O. Box 56, 00014, University of Helsinki, Finland.
authors.forename: Tiina J
authors.initials: TJ
authors.lastname: Kauppila
mesh_terms: D000818:Animals; D001274:Atmospheric Pressure; D001564:Benzo(a)pyrene / Q000032:analysis / Q000737:chemistry; D001577:Benzophenones; D002417:Cattle; D007659:Ketones; D013058:Mass Spectrometry / Q000295:instrumentation* / Q000379:methods*; D046208:Microchip Analytical Procedures; D008892:Milk / Q000737:chemistry; D011092:Polyethylene Glycols; D011108:Polymers; D013193:Stainless Steel; D014050:Toluene / Q000737:chemistry; D014280:Triglycerides / Q000032:analysis / Q000737:chemistry
chemical_list: D001577:Benzophenones; D007659:Ketones; D011108:Polymers; D014280:Triglycerides; D013193:Stainless Steel; C063834:polyetheretherketone; D001564:Benzo(a)pyrene; D014050:Toluene; D011092:Polyethylene Glycols