Gas-Phase Reactions of Laser-Desorbed Molecules with Ions from Electrospray

Abstract

Gas-phase reactions of neutral molecules delivered by laser desorption with ions introduced via an electrospray interface have been observed. To maximize the production of neutrals while keeping laser ionization products negligible, the laser fluence has been adjusted only slightly above the ionization threshold fluence. The reactions have been performed in the entrance to an ion funnel operated at 3-4 mbar. Both the laser desorption assembly and the electrospray interface belong to an electrospray ionization to matrix-assisted laser desorption/ionization switchable combination ion source attached to a Fourier transform ion cyclotron resonance mass spectrometer. The reaction products of molecular species of 1-aza[6]-helicene, 1,8-dihydroxy-9-anthrone (dithranol) and 2-mercaptobenzothiazole with protonating reagent ions and silver cations from electrospray were detected. The products were identified by their accurate mass, proton/deuterium isotopic exchange and by resolving the corresponding peaks of isotopolog ions.

A Liquid Injection Field Desorption/Ionization-Electrospray Ionization Combination Source for a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer

“…Under these conditions, the residual gas is still capable of thermalizing the ions (p.88 in [31]), a property particularly valuable to cool the fast ions emerging from the MALDI target. This ion source is even capable of simultaneously admitting ions from its ESI and (MA)LDI units into the ion funnel-an admittedly rare mode of operation that has recently been demonstrated to allow for ion-molecule reactions of laser-desorbed neutrals with electrosprayed ions [32].…”

Molecular ion formation on activated field emitters in atmospheric pressure field desorption mass spectrometry

“…In contrast to the hydrocarbons examined so far, 1-aza[6]helicene is a polycyclic aromatic pyridine base [ 44 , 45 ] with a known high proton affinity of 1000 kJ mol –1 [ 43 ]. This compound had been studied in laser desorption ionization (LDI) where laser desorbed neutrals were shown to undergo gas phase protonation with ions from electrospray within the ion source housing [ 42 ].…”

“…2 . Anthracene (CAS 120–12-7) and benzo[a]pyrene (CAS 50–32-8) were from Sigma-Aldrich (Steinheim, Germany), 1,1,4,4-tetraphenylbutadiene (CAS 1450–63-1) from Fluka (Buchs, Switzerland), fluoranthene (CAS 206–44-0) from Bruker Daltonics (Bremen, Germany), and 1-aza[6]helicene was preserved from a previous study [ 42 ]. The sample had originally been obtained as a gift for mass spectral studies [ 43 – 45 ].…”