Mathematisch-Naturwissenschaftliche Fakultät

Institut für Chemie

Fachgebiet: Analytical Chemistry

Betreuer: Prof. Dr. Ralf Zimmermann

Sven Ehlert
(e-mail: )

Detection of security relevant substances via soft ionization mass spectrometric methods using ambient pressure laser desorption

Global terrorism, terroristic attack, organized crime or clandestine drug laboratories are recent dangers in our globalized, fast and connected world. Thus it is even more important to develop fast, secure, sensitive, selective and above all reliable analytical method to detect these common threats. Within this work there was on the one hand the focus on a steadily sampling method especially for substances having a low vapor pressure and partially combined with a thermal instability. Into this classification many of the common explosives need to be sorted, but also some of common narcotics appearing as salt compounds such as the cocaine hydrochloride. On the other hand, it was planned to have a view on selectivity enhancement to get reliable results and increase the confidence of an operator to the results.

The first aim could be solved introduce Ambient Pressure Laser Desorption (APLD) sampling. Using 4 ns short pulsed laser radiation of 532 nm wavelength enables direct shockwave ablation of target molecules from an investigated surface. The desorbed analyte molecules can be analyzed with varying analytical instruments. However, for practical and security reasons the laser radiation was coupled to glassy fibers to reach hidden surfaces for instance inside of shipping containers, boxes or pieces of luggage.

The second objective was covered by investigating soft ionization techniques such as Single Photon Ionization (SPI) or Chemical Ionization (CI) in an Ion Trap Mass Spectrometer (IT-MS). For a wide range of narcotics SPI allows a very selective, fragment free ionization with simultaneous suppression of matrix molecules such as nitrogen, oxygen or gaseous water. Additionally, to reach a further enhancement of selectivity and more reliable substance identification the MSn capability of the used IT-MS system was used. It allows a conscious fragmentation of an analyte mass getting an accessorily fragment fingerprint spectra to verify an identification.

Using APLD coupled with soft ionization mass spectrometric methods enables especially for security relevant substances with low vapor pressure an enhancement for an early detection and identification of potential threats.