In this contribution two analytical devices for the fast detection of security-relevant substances like narcotics and explosives
are presented. One system is based on an ion trap mass spectrometer (ITMS) with single photon ionization (SPI).
This soft ionization technique, unlike electron impact ionization (EI), reduces unwanted fragment ions in the mass spectra
allowing the clear determination of characteristic (usually molecular) ions. Their enrichment in the ion trap and identification
by tandem MS investigations (MS/MS) enables the detection of the target substances in complex matrices at
low concentrations without time-consuming sample preparation. For SPI an electron beam pumped excimer light source
of own fabrication (E-Lux) is used. The SPI-ITMS system was characterized by the analytical study of different drugs
like cannabis, heroin, cocaine, amphetamines, and some precursors. Additionally, it was successfully tested on-site in a
closed illegal drug laboratory, where low quantities of MDMA could be directly detected in samples from floors, walls
and lab equipments. The second analytical system is based on an ion mobility (IM) spectrometer with resonant multiphoton
ionization (REMPI). With the frequency quadrupled Nd:YAG laser (266 nm), used for ionization, a selective
and sensitive detection of aromatic compounds is possible. By application of suited aromatic dopants, in addition, also
non-aromatic polar compounds are accessible by ion molecule reactions like proton transfer or complex formation. Selected
drug precursors could be successfully detected with this device as well, qualifying it to a lower-priced alternative
or useful supplement of the SPI-ITMS system for security analysis.
Elisabeth Schramm, Thomas Heindl, Jasper Hölzer, Alexander McNeish, Michael Puetz, Hermann Ries, Patricia Schall, Rasmus Schulte-Ladbeck, Rainer Schultze, Martin Sklorz, Gerd Spieker, Roman Trebbe, Andreas Ulrich, Jochen Wieser, Ralf Zimmermann
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.
Elisabeth Schramm, Stephan Borrmann, Joachim Curtius, Andreas Goertler, Thomas Heindl, Andreas Kuerten, Alexander McNeish, Stefan Mitschke, Andrei Morozov, Fabian Muehlberger, Michael Puetz, Gerd Reichardt, Hermann Ries, Patricia Schall, Rasmus Schulte-Ladbeck, Rainer Schultze, Martin Sklorz, Roman Trebbe, Andreas Ulrich, Jochen Wieser, Ralf Zimmermann
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.
Quantitative analysis of unknown PAH contaminated soil samples have been performed using laser-induced fluorescence (LIF) spectroscopy and strategies for a safe application of calibration routines under field conditions have been developed. Influences of varying matrix properties have been investigated using LIF and diffuse reflectance (DR) spectroscopy. A petroleum hydrocarbon contaminated former military site has been investigated and the results from the on-site LIF measurements are compared to the results of additional laboratory analysis. A three dimensional dataset of analyte concentrations has been prepared and extent, distribution and origin of the contamination are discussed. A fiber optical probe for in situ LIF-investigations in the subsurface has been developed. The probe has been tested in investigations of soil columns and within in situ measurements at a former gas work site.
The drift time spectra of polycyclic aromatic hydrocarbons (PAH), alkylbenzenes and alkylphenylethers were recorded with a laser-based ion mobility (IM) spectrometer. The ion mobilities of all compounds were determined in helium as drift gas. This allows the calculation of the diffusion cross sections (Ωcalc) on the basis of the exact hard sphere scattering model (EHSSM) and their comparison with the experimentally determined diffusion cross sections (Ωexp). These Ωexp/Ωcalc-correlations are presented for molecules with a rigid structure like PAH and prove the reliability of the theoretical model and experimental method. The increase of the selectivity of IM spectrometry is demonstrated using resonance enhanced multiphoton ionisation (REMPI) at atmospheric pressure, realized by tuneable lasers. The REMPI spectra of nine alkylbenzenes and alkylphenylethers are investigated. On the basis of these spectra, the complete qualitative distinction of eight compounds in a mixture is shown. These experiments are extended to alkylbenzene isomer mixtures.
Photophysical properties of the widely used fluorescence tracers eosin, uranin and pyranine were determined in water at different pH. In order to elucidate the potential of LIF spectroscopy for in-situ measurements, calibration curves of uranin in different waters have been measured and the influence of other components in natural waters and of soil on the LIF signals was determined. Furthermore, LIF spectroscopy was applied to the investigation of sorption processes in water/soil-mixtures and of transport processes in soil columns.
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