A new atmospheric pressure (AP) infrared (IR) matrix-assisted laser desorption/ionization (MALDI) ion source was developed and interfaced with a Thermo Finnigan LCQ ion trap mass spectrometer. The source utilized a miniature all-solid-state optical parametric oscillator (OPO)-based IR laser system tunable in the ϭ 1.5-4 m spectral range and a nitrogen ultraviolet (UV) laser ( ϭ 337 nm) for use in comparative studies. The system demonstrated comparable performance at 3 m and 337 nm wavelengths if UV matrices were used. However, AP IR-MALDI using a 3 m wavelength showed good performance with a much broader choice of matrices including glycerol and liquid water. AP IR-MALDI mass spectra of peptides in the mass range up to 2000 Da were obtained directly from aqueous solutions at atmospheric conditions for the first time. A potential use of the new AP IR-MALDI ion source includes direct MS analysis of biological cells and tissues in a normal atmospheric environment as well as on-line coupling of mass spectrometers with liquid separation techniques. (J Am Soc Mass Spectrom 2002, 13, 354 -361)

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Fragmentation of protonated peptide ions via interaction with low kinetic energy electronicallyexcited metastable argon atoms was studied in a linear trap-time-of-flight mass spectrometer. Metastable argon atoms were generated using a glow discharge-type source. Protonated peptide ions of substance P, bradykinin, fibrinopetide A, and insulin oxidized chain B were produced by electrospray ionization and trapped in a quadrupole ion guide for 100-400 ms. Intensive series of c- and z-ions were observed in all cases. The kinetic measurements of the fragmentation rates are consistent with calculations of the reaction cross section based on the Landau-Zener approximation.

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