title: Laserspray ionization imaging of multiply charged ions using a commercial vacuum MALDI ion source.
abstract: This is the first report of imaging mass spectrometry (MS) from multiply charged ions at vacuum. Laserspray ionization (LSI) was recently extended to applications at vacuum producing electrospray ionization-like multiply charged ions directly from surfaces using a commercial intermediate pressure matrix-assisted laser desorption/ionization ion mobility spectrometry (IMS) MS instrument. Here, we developed a strategy to image multiply charged peptide ions. This is achieved by the use of 2-nitrophloroglucinol as matrix for spray deposition onto the tissue section and implementation of "soft" acquisition conditions including lower laser power and ion accelerating voltages similar to electrospray ionization-like conditions. Sufficient ion abundance is generated by the vacuum LSI method to employ IMS separation in imaging multiply charged ions obtained on a commercial mass spectrometer ion source without physical instrument modifications using the laser in the commercially available reflection geometry alignment. IMS gas-phase separation reduces the complexity of the ion signal from the tissue, especially for multiply charged relative to abundant singly charged ions from tissue lipids. We show examples of LSI tissue imaging from charge state +2 of three endogenous peptides consisting of between 1 and 16 amino acid residues from the acetylated N-terminal end of myelin basic protein: mass-to-charge (m/z) 795.81 (+2) molecular weight (MW) 1589.6, m/z 831.35 (+2) MW 1660.7, and m/z 917.40 (+2) MW 1832.8.
authors.affiliation: Department of Chemistry, Wayne State University, Detroit, Michigan 48202, United States.
authors.forename: Ellen D
authors.initials: ED
authors.lastname: Inutan
authors.forename: James
authors.initials: J
authors.lastname: Wager-Miller
authors.forename: Ken
authors.initials: K
authors.lastname: Mackie
authors.forename: Sarah
authors.initials: S
authors.lastname: Trimpin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000378:metabolism; D007834:Lasers; D051379:Mice; D057054:Molecular Imaging / Q000379:methods*; D008969:Molecular Sequence Data; D004676:Myelin Basic Protein / Q000737:chemistry / Q000378:metabolism; D011312:Pressure; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014618:Vacuum
chemical_list: D004676:Myelin Basic Protein