Explosive Detection Using Plasma-Assisted Desorption Ionization (PADI)
For fast and dependable detection of explosives
Safe and effective detection of explosives depends on the ability to identify trace quantities of explosive materials rapidly. Hiden Analytical mass spectrometry systems facilitate versatile and sensitive explosive detection in real-time using plasma-assisted desorption ionization (PADI).
The ability to detect common explosive compounds is of paramount importance for security applications. Reliability is a required feature of all explosive detection systems; however, many applications – air travel in particular – also demand high detection speed and low sample preparation requirements.
Plasma-assisted desorption ionization (PADI) is one such technique, offering rapid and sensitive detection of explosive molecules without any requirement for sample preparation.1,2
PADI uses dielectric barrier discharge (DBD) to produce a non-thermal atmospheric-pressure plasma jet. This means that, unlike in other plasma-based techniques, the plasma can be safely introduced directly to a sample under ambient conditions and without any damage to the sample.
The plasma jet both ionizes and desorbs molecules directly from the sample surface, at which point a mass spectrometer can detect ionized species. The characteristic mass spectra obtained can then be compared with those of explosive materials. Many common explosive compounds – including trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), and triacetone triperoxide (TATP) – can be detected to trace levels using this technique.
Explosive Detection with Hiden Analytical
The sample throughput rate achieved by a PADI detection system is limited by the speed of the mass spectrometry system used. The Hiden Analytical HPR-60 is an atmospheric quadrupole mass spectrometer optimized for plasma analysis. Researchers used the HPR-60 to achieve direct analysis in real-time thanks to its ability to sample continuously and obtain spectra for each sample in seconds.1
Example plasma-assisted positive ion mass spectrum of some typical explosive compounds.
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Plasma Assisted Desorption Ionisation for the detection of pharmaceutical compounds
A novel plasma-assisted desorption/ionization (PADI) method that can be coupled with atmospheric pressure sampling mass spectrometry to yield mass spectral information under ambient conditions of pressure and humidity from a range of surfaces without the requirement for sample preparation or additives is reported. PADI is carried out by generating a nonthermal plasma which interacts directly with the surface of the analyte. Desorption and ionization then occur at the surface, and ions are sampled by the mass spectrometer. The PADI technique is demonstrated and compared with desorption electrospray ionization (DESI) for the detection of active ingredients in a range of over-the-counter and prescription pharmaceutical formulations, including nonsterodial antiinflammatory drugs (mefenamic acid, Ibugel, and ibuprofen), analgesics (paracetamol, Anadin Extra), and Beecham’s “all in one” cold and flu remedy. PADI has also been successfully applied to the analysis of nicotine in tobacco and thiosulfates in garlic. PADI experiments have been performed using a prototype source interfaced with a Waters Platform LCZ single-quadrupole mass spectrometer with limited modifications and a Hiden Analytical HPR-60 molecular beam mass spectrometer (MBMS). The ability of PADI to rapidly detect active ingredients in pharmaceuticals without the need for prior sample preparation, solvents, or exposed high voltages demonstrates the potential of the technique for high-throughput screening in a pharmaceutical or forensic environment.
Anal.Chem 2007 79, 6094-6101 https://pubmed.ncbi.nlm.nih.gov/17628043/
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Description of HiPIMS plasma regimes in terms of composition, spoke formation and deposition rate
The behaviour of Cu and Cr HiPIMS (high power impulse magnetron sputtering) discharges was investigated by a combination of optical emission spectroscopy, energy-resolved mass spectrometry and optical imaging, for the complete current–voltage characteristic range achievable within our experimental conditions. Inflection points typical of HiPIMS current–voltage characteristics separate plasma regimes perfectly differentiated in terms of flux composition of species towards the substrate, deposition rate, and the nature of plasma self-organization. The reorganization of the HiPIMS plasma into spokes (areas of high ionization over the target) is associated to one regime of high plasma conductivity, where also deposition rate is limited. This spoke-dominated regime can be substituted by a homogeneous regime at higher powers, where there is an increase of deposition rate, which is driven mostly by an increase in the flux of metal neutrals and metal double-charged ions. The relevance of secondary electron emission mechanisms for the support of the spoke-dominated regime in reactive and non-reactive sputtering conditions is discussed.
Teresa de los Arcos, Raphael Schroder, Yolanda Aranda Gonzalvo, Volker Schulz-von der Gathen and Jorg Winter (Published 25 September 2014)
Online at: http://stacks.iop.org/0963-0252/23/054008
Whitmore, T. D. et al. Surface analysis by plasma assisted desorption ionisation mass spectrometry (PADI-MS). 3 (2007).
Salter, T. L., Gilmore, I. S., Bowfield, A., Olabanji, O. T. & Bradley, J. W. Ambient Surface Mass Spectrometry Using Plasma-Assisted Desorption Ionization: Effects and Optimization of Analytical Parameters for Signal Intensities of Molecules and Polymers. Anal. Chem. 85, 1675–1682 (2013).
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