Development of laser -based evaporation methods for Fourier -transform ion cyclotron resonance mass spectrometry

A probe-mounted fiber optic assembly was designed and constructed to allow laser desorption (LD) in transmission geometry (back-side irradiation of the sample through a transparent support) inside mass spectrometers equipped with a commercial solids probe inlet. The apparatus was used to employ transmission mode LD for the first time inside a Fourier-transform ion cyclotron resonance mass spectrometer. It was found that the average velocity measured for ions evaporated by transmission mode LD is about half the velocity of those obtained by using the reflection geometry. Therefore, it was concluded that transmission mode irradiation of the sample results in the evaporation of ions that are easier to trap in an ICR cell. Laser-induced acoustic desorption (LIAD) of neutral molecules coupled with electron and chemical ionization was examined as an analysis method for non-volatile organic and biomolecules in Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry. The experiments were carried out with the probe designed for transmission mode laser desorption. The applicability of the method was demonstrated for a wide variety of molecules, including an organic salt, steroids, sugars, oligopeptides, nucleic acid bases, nucleosides, and synthetic polymers. It was concluded that LIAD combined with post-desorption ionization in an FT-ICR shows promise as a practical method for the analysis of thermally labile, non-volatile molecules. The performance of a small FT-ICR mass spectrometer was investigated for its utility in experiments involving laser-based evaporation of samples (e.g., MALDI). It was found that the trapping efficiency of this low-field instrument was inadequate for MALDI experiments. The implementation of ion axialization methods did not improve trapping efficiency of MALDI generated ions