Mass spectrometry is based on the detection of gaseous ions carrying with either positive charges or negative charges.  Matrix-assisted laser desorption ionization (MALDI), electrospray (ESI) and electron impact (EI) have been developed for the production of ions that can be detected by mass spectrometers.  Among these techniques, EI is called a hard ionization in which highly energetic electrons interact with gaseous neutral molecules to produce ions.  We are describing herein a new electron-directed ionization techniques based on laser activated interfacial photoelectron transfer.  It has been found that tunneling photoelectrons on surfaces of semiconductor materials irradiated with the 3rd harmonic of Nd3+:YAG laser (355 nm) can be exothermally captured by adsorbed molecules.  By controlling kinetic energies of photoelectrons, associative/dissociative electron capture as well as electron detachment have been observed.  In such approach, resultant radical anions undergo very specific fragmentations because of significantly decreased vibrational excitation.  Compared with EI in which the kinetic energies of impact electrons have to be set above 20 eV in order to increase ionization efficiency although high kinetic energies causes vibrational excitation, the capture of interfacial photoelectrons is an exothermal processes that can proceed spontaneously.  Therefore the ionization and dissociation can be performed under very low bias voltages with high ionization efficiency.  By using this principle, we have established a new technique for mass spectrometric imaging with improved spatial resolution and capabilities for structural identification.

Soft ionization and dissociation based on laser activated interfacial photoelectron transfer for mass spectrometry

2019 Fall National Meeting

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