IR-MALDI Ion Mobility Spectrometry: Characterization and applications

Infrared matrix-assisted laser dispersion and ionization (IR-MALDI) is a soft ionization technique which enables the direct analysis of a wide range of biologically relevant molecules in aqueous solution. IR-MALDI is based on the release of ions by liquid dispersion through the excitation of the OH-stretch vibration band of water by an IR laser pulse (λ = 2.94 µm). For this work the dispersion process at atmospheric pressure, stemming from a laser-induced phase explosion, has been thoroughly studied and characterized by means of shadowgraphy and ion mobility (IM) spectrometry. The focus of the investigations was on the phase explosion-induced transport of ions and peak formation in IM spectra. Furthermore, the speed of the phase explosion-induced transport of ions could be determined. As a result of our studies the spectrometer was optimized, and limits of detection as low as 5 nmol/L and linear ranges of 2-3 orders of magnitude were obtained. The potential of IR-MALDI IM spectrometry to analyze simple mixtures by the stand-alone spectrometer and more complex mixtures after preseparation on an HPLC column is illustrated.