Laser Ionization Ion Mobility – A New System for Selective Detection of Chemicals

Ion Mobility Spectrometers (IMS) are widely used to detect chemical threats. The systems are for example used at airports to detect explosives or drugs, handheld IMS systems are also used by military forces as a warning system against chemical warfare agents. Compared to mass spectrometry they do operate at ambient pressures and therefore the ionization is also a chemical ionization where at the end only compounds with very high proton affinity (in positive mode) or electron negativity (negative mode) can be measured. Usually, they use radioactive ion sources or corona discharge ion sources, which at the first step do ionize everything in air. These types of instruments are not very useful for a selective detection of specific compounds in mixtures. Therefore, often a pre-separation, such as gas chromatography, is required.

In this presentation an alternative method is developed, with the goal to selectively ionize and detect specific compounds. We developed a laser ionization technique based on Resonance-Enhanced-Multiphoton Ionization (REMPI) to ionized specific compounds. A further characterization of those selective ionized compounds will then be conducted by performing a mobility experiment by measuring the drift time in an atmospheric pressure IMS.
The developed instrument will be described as well as first applications. While the system is still under development, initial results indicate significant potential to selectively measure polycyclic aromatic compounds (PAH) in the environment. Other applications such as the selective identification of illicit drugs will also be discussed.