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- Ambient ionization (2) (entfernen)
Organisationseinheit der BAM
Recently, a novel ionization scheme for ambient MS has been introduced. It is based on a quasi-continuous laser induced plasma (LIP), ignited in front of the MS inlet. This setup comprises the advantages of an ambient probe, electro neutrality, a sufficient duty cycle, a ubiquitous plasma medium, low power consumption, the absence of solvents and high sensitivity. To assess its future applicability for the detection of volatile organic compounds, plasma properties and operating conditions are investigated to understand the processes, that lead to the unexpected formation of intact molecular ions. Comprehensive studies include optical Emission spectroscopy, shadowgraphic shockwave visualization and time-of-flight mass spectrometry.
An airborne high repetition rate laser-induced plasma was applied as a versatile ambient ionization source for mass-spectrometric determinations of polar and nonpolar analytes in solution. The laser plasma was sustained between a home-built pneumatic nebulizer and the inlet capillary of an Orbitrap mass spectrometer. To maintain stable conditions in the droplet-rich spray environment, the plasma was directly fed by the fundamental output (λ = 1064 nm) of a current state-of-the-art diode-pumped solid-state laser. Ionization by the laser-driven plasma resulted in signals of intact analyte ions of several chemical categories. The analyte ions were found to be fully desolvated since no further increase in ion signal was observed upon heating of the inlet capillary. Due to the electroneutrality of the plasma, both positive and negative analyte ions could be formed simultaneously without altering the operational parameters of the ion source. While, typically, polar analytes with pronounced gas phase basicities worked best, nonpolar and amphoteric compounds were also detected. The latter were detected with lower ion signals and were prone to a certain degree of fragmentation induced during the ionization process. All the described attests the laser-induced microplasma by a good performance in terms of stability, robustness, sensitivity, and general applicability as a self-contained ion source for the liquid sample introduction.