High-Pressure Gas Phase Femtosecond Laser Ionization Mass Spectrometry

We describe a novel ion source for analytical mass spectrometry based on femtosecond laser ionization at pressures at and above atmospheric and characterize its performance when coupled to a tandem quadrupole/time-of-flight mass spectrometer. We assess source saturation limits, ionization and sampling efficiencies, the effective ionization volume, and limits of detection. We demonstrate 100% efficient ionization for a set of organic compounds and show that the degree of ion fragmentation over a range of laser powers is favorable compared to electron impact ionization, especially in that a substantial parent ion signal is always observed. We show how collisional cooling plays a role in controlling fragmentation at high pressures and address how ion−molecule chemistry can be controlled or exploited. High- pressure femtosecond laser ionization will allow "universal" and efficient ionization, presenting a research direction that will broaden the options for gas phase analysis beyond the capabilities of electron impact ionization.