Detection of security relevant substances within the cooperative project SAFE XUV

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.