title: Infrared laser post-ionization of large biomolecules from an IR-MALD(I) plume.
abstract: A two-infrared laser desorption/ionization method is described. A first laser, which was either an Er:YAG laser or an optical parametric oscillator (OPO), served for ablation/vaporization of small volumes of analyte/matrix sample at fluences below the ion detection threshold for direct matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). A second IR-laser, whose beam intersected the expanding ablation plume at a variable distance and time delay, was used to generate biomolecular ions out of the matrix-assisted laser desorption (MALD) plume. Either one of the two above lasers or an Er:YSGG laser was used for post-ionization. Glycerol was used as IR-MALDI matrix, and mass spectra of peptides, proteins, as well as nucleic acids, some of which in excess of 10(5) u in molecular weight, were recorded with a time-of-flight mass spectrometer. A mass spectrum of cytochrome c from a water ice matrix is also presented. The MALD plume expansion was investigated by varying the position of the post-ionization laser beam above the glycerol sample surface and its delay time relative to the desorption laser. Comparison between the OPO (pulse duration, tau(L) = 6 ns) and the Er:YAG laser (tau(L) approximately 120 ns) as primary excitation laser demonstrates a significant effect of the laser pulse duration on the MALD process.
authors.affiliation: Institute of Medical Physics and Biophysics, Westfälische-Wilhelms Universität, Muenster, Germany.
authors.forename: Arne
authors.initials: A
authors.lastname: Leisner
authors.forename: Andreas
authors.initials: A
authors.lastname: Rohlfing
authors.forename: Stefan
authors.initials: S
authors.lastname: Berkenkamp
authors.forename: Franz
authors.initials: F
authors.lastname: Hillenkamp
authors.forename: Klaus
authors.initials: K
authors.lastname: Dreisewerd
mesh_terms: D000803:Angiotensin I / Q000737:chemistry; D045304:Cytochromes c / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D007053:Ice; D007074:Immunoglobulin G / Q000737:chemistry; D007259:Infrared Rays; D007477:Ions / Q000737:chemistry; D007834:Lasers; D011506:Proteins / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
chemical_list: D007053:Ice; D007074:Immunoglobulin G; D007477:Ions; D011506:Proteins; D045304:Cytochromes c; D004247:DNA; D000803:Angiotensin I