Femtosecond Laser Desorption Postionization Mass Spectrometry Imaging of Geological Samples

Ultrashort pulses from femtosecond (fs) lasers can be used to ablate any material regardless of the target’s optical properties. Another important aspect of fs laser pulses is that, while ablating material from a sample surface, they do minimal or no damage to the underlying material. Single-photon ionization is a universal ionization mechanism of molecules that is less constrained by molecules’ structural and electronic properties. A newly designed time-of-flight mass analyzer has been built and implemented on the custom-built laser desorption postionization (LDPI) mass spectrometer in the Hanley group, replacing the old reflectron time-of-flight mass analyzer with a new time-of-flight referred to as a right angle ion mirror prism (RAIMP). A fluorine excimer laser was also added as a photoionization laser. The 7.9 eV fs-LDPI mass spectrometry utilizes 800 nm, <100 fs desorption pulses combined with 157 nm, 7.9 eV photon energies from the fluorine excimer laser for single-photon ionization. The 7.9 eV fs-LDPI technique can be used to analyze various samples, including test mixtures, drug compounds, and geological samples. The performance of the new LDPI RAIMP-TOF mass spectrometer is evaluated and documented regarding mass resolution and accuracy. Three drug compounds that show low ionization efficiencies in secondary ion mass spectrometry have been successfully detected and analyzed. The ability of fs-LDPI mass spectrometry on analyzing geological samples is demonstrated and discussed in terms of performing targeted analysis, removing surface contaminants, and excavating into the sample to uncover organic components and hence biomarkers.