Desorption/ionization of biomolecules from aqueous solutions at atmospheric pressure using an infrared laser at 3 μm

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Abstract
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 λ = 1.5–4 μm spectral range and a nitrogen ultraviolet (UV) laser (λ = 337 nm) for use in comparative studies. The system demonstrated comparable performance at 3 μm and 337 ran wavelengths if UV matrices were used. However, AP IR-MALDI using a 3 μm 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.

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