Real-time trace detection of security-relevant compounds in complex sample matrices by thermal desorption–single photon ionization–ion trap mass spectrometry (TD-SPI-ITMS) Spectrometry (TD-SPI-ITMS)

For the detection of security-relevant substances at low concentrations in complex matrices, coupling of thermal desorption–single photon ionization–ion trap mass spectrometry (TD-SPI-ITMS) was successfully tested. The main advantage of taking solid samples with a wipe pad followed by thermal desorption is the low detection limit by enhanced vapor pressure. Single photon ionization is a soft ionization technique which reduces the target ion fragmentation and shields bulk components with high ionization energies (IE) like nitrogen yielding to clearly arranged mass spectra with significant high mass peaks. To obtain low false-positive and false-negative rates, especially necessary for security-relevant substances, the ion trap mass spectrometer allows identification of signals with MS/MS studies. In this concept, the soft ionization technique fits well with the MS/MS studies, as peaks with high masses are generated yielding significant MS/MS fragments. For the ionization, photon energies between about 8 eV (155 nm) and 12 eV (103 nm) were generated with electron-beam-pumped rare gas excimer lamps (EBEL). Depending on the rare gas used, light with different photon energy is generated, adapted to the substances of interest. So, even most narcotics, having relatively low IEs, can be ionized with 8.4 eV photons without massive fragmentation. For most explosives, photons with higher energy must be used as their IEs are higher. In this work, a mobile setup with a commercial ion trap mass spectrometer has been developed and tested. Even a first real-scenario measurement campaign was accomplished successfully proving the field-suitability of the system.