The objective of this accomplished project funded by the German BMBF was to develop a single photon ionization ion
trap mass spectrometer (SPI-ITMS) for detection of security relevant substances in complex matrices at low
concentrations. The advantage of such a soft ionization technique is a reduction of target ion fragmentation allowing
identification of signals from complex matrices and enabling MS/MS capability. To obtain low detection limits, the
applied photon energy has to be below the ionization potential (IP) of the bulk matrix components. Therefore, photon
energies between 8 eV (155 nm) and 12 eV (103 nm) are necessary which was achieved with newly developed electron
beam excimer lamps (EBEL). They generate light at different wavelengths depending on the selected rare gas emitting
wavelengths adapted to the analyzed substances. So, e.g. with a krypton-EBEL with 8.4 eV photon energy most narcotics
can be ionized without notable fragmentation. Due to their higher IPs, EBEL with higher photon energy have to be used
for most explosives. Very low false-positive and false-negative rates have been achieved using MS/MS studies. First
field tests of a demonstrator provided the proof of principle.
The objective of this project funded by the German BMBF was to show that security relevant substances can be detected
in complex matrices at low concentrations using single photon ionization ion trap mass spectrometry (SPI-ITMS). The
advantage of such a soft ionization technique is a reduction of unwanted fragment ions in mass spectra allowing
identification of signals from complex matrices and enabling MS/MS capability. The MS/MS studies permit low false-positive
and false-negative rates. Additionally, the accumulation of the ions in the ion trap decreases the detection limit.
To obtain low detection limits the ionization potentials (IPs) of the relevant substances have to be below the IPs of the
bulk matrix components. That enables the utilization of a photon energy unaffecting the matrix components resulting in
increased sensitivity due to essentially non-existent background signals. As literature values for many ionization
potentials are unavailable, IPs of several security relevant substances were determined using monochromatized
synchrotron radiation from BESSY, Germany. All analyzed substances exhibited IPs significantly below the IPs of
common matrix molecules such as water, nitrogen and oxygen. First measurements with a pre-demonstrator show that it
is possible to shield matrix substances using a well chosen photon energy for soft ionization.