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Forensic analysis of explosives
Youngeun Choi, Dario Remmler, Maximilian Ries, Felix Rsicke, Radwan Sarhan, Felix Stete, Zhiyang Zhang
Detecting and identifyingexplosives is of great importance
Airport and airline security
Demining
Forensic analysis
Removal of unexploded ordnance
Picture: Wo st 01/Wikipedia
Picture: MatthiasKabel/Wikipedia
Picture: Tom Oates/Wikipedia
Picture: Mark A. Moore/Wikipedia
Outline
Forensic analysis
Common explosives
Inorganic explosives examples and sample preparation
selected analytical techniques
Organic explosives containing Nitro-moieties Principle of detection
selected analytical techniques
Other important explosives
Forensic analysis
After an incident with an explosion:
Where was the source of the explosion?
Which explosive was used?
Where did the explosive come from?
Commonly used explosives
Inorganic explosives: Explosives with containing Nitro-moieties:
Others:
Ammonium nitrate
+ S + CK++
Black powder
Trinitrotoluene (TNT)
Nitroglycerin (NG)
Triacetone triperoxide (TATP)
Dust of flammable materials
Inorganic Explosives
Type Decomposition mechanism Characteristic ions
Ammonium nitrate 2 NH4NO3 4 H2O + 2 N2 + O2 NO3, NH4+
Ammonium perchlorate 2 NH4ClO4 Cl2 + 2 O2 + N2 + 4 H2O NO3, ClO4-, NH4+
Pure compounds
Ignition needed!
Inorganic Explosives
Type Composition Characteristic ions
ANFO(Ammonium nitrate fuel oil)
NH4NO3, fuel oil (long chain hydrocarbons)
NO3, NH4+, MeNH3+
Black powder Nitrates, sulfur, charcoal NO3, SO42-, S2O32
Na+, K+
Chlorate blends Chlorates, reducing agent(Metal powders, sugars etc.)
ClO3-, Cl-, Al3+, Na+, K+
Perchlorate blends Perchlorates, reducing agent(Metal powders, sugars etc.)
ClO4-, Cl-, Al3+, Na+, K+
Pure compounds Mixtures
Oxi
dizin
gsa
lt/ fu
el
Inorganic Explosives
Sample preparation:
Inorganic compounds: salts - soluble in water
Dissolve in water!
(removal of organic compounds if necessary)
further preparation strongly dependent on applied method
Source: Youtube
Inorganic Explosives
On-site analytics Colorimetric reactions (wet-chemical ion specific reactions)
Brown ring reaction: NO3-
Berthelot reaction: NH4+
Flame colouring
https://de.wikipedia.org/wiki/Ringprobe
Reaction Ion LOD Source
Brown ring NO3- 30 g/ml Stevens 1966
Berthelot reaction NH4+ 10 ng/ml Tsuboi et al. 2002
http://www.chemische-experimente.com/Alkalimetalle.htm
Hubalek et al. 2007
Inorganic Explosives
Off-site analytics Ion Exchange Chromatography
fast only quantitative when ion separate clearly
Desorption Electro Flow-Focusing Ionization(DEFFI)-MS with CID CID improves selectivity by breaking up adducts - elemental
ions can be preduced and detected more selectively includes mapping possibilities high instrumental effort
Technique Ion LOD Source
IECAl3+
ClO3-ClO4-
0.95 ng/l2 ng/ml
0.77 ng/ml
Gibson et al. 1991Binghui et al. 2006
Tian et al. 2003
DEFFI-MS K+Pb+
ClO3-
10 ng1 ng
300 pgForbes et al. 2014
Source: Forbes et al. 2014
Nitro compounds
Trinitrotoluene (TNT)
Nitroglycerin (NG)
Explosives with nitro-groups:
2 C7H5N3O6(s) 12 CO(g) + 5 H2(g) + 3 N2(g) +2 C(s)
Violent decomposition of TNT:
Relative to 1 kg TNT
TNT 1
Black powder 0,55
Dynamite 1,54
RDX 1,60
Octanitrocubane 2,38
Nuclear bomb (Nagasaki) 4500
R.E. Factor: Relates an explosives demolition power to that of TNT
Mass Spectrometry exibits extraordinary properties in explosive detection
Mass Spectrometry
QuadrupoleIontrap
Time-of-flight (TOF)Tandem based (MS/MS)
Modes
IonizationMatrix-assisted laser desorption/ionization
Electrospray ionizationChemical ionization
...
Detection Limits
2,4,6-trinitrotoluene (TNT)* 3 pg/L
2,4-dinitrotoluene (DNT)* 90 ng/L
1,3,5-trinitro-1,3,5-triazacyclohexane* 1 ng
PETN** 1 ng
Source: * Current trends in explosive detection techniques J. Sarah Caygill, Frank Davis, Seamus P.J. Higson
** Direct detection of explosives on solid surfaces by mass spectrometry with an ambient ion source based on dielectric barrier discharge Na Na, Chao Zhang, Mengxia Zhao, Sichun Zhang, Chengdui Yang, Xiang Fang, Xinrong Zhang
Direct Analysis in Real Time is very useful forexamining surfaces
Direct Analysis in Real Time (DART)
Mechanism in Detail: Penning Ionization
M*+ S S+ + M + e-
He(23S) + H2O H2O++ He(11S) + electronH2O++H2O H3O++ OH
H3O++ n H2O [(H2O)nH]+[(H2O)nH]++ S SH++nH2O
Source: Direct Analysis in Real Time (DARTtm) Mass Spectrometry Robert B. Cody, James A. Larame, J. Michael Nilles, H. Dupont Durst
Sample
Atmospheric-pressure chemical ionizationuses high temperatures for sampling
Atmospheric pressure chemical ionization interface (APCI)
Advantages:
- soft ionization method - reduces the thermal decomposition- possible to use a nonpolar solvent
Source: https://en.wikipedia.org/wiki/Atmospheric-pressure_chemical_ionization
Disadvantage:
- sample has to be in solution
ESI/quadrupole HMX;RDX;PETN;Tertyl 170 fmol/L Straub & Voyksner, 1993
APCI;MS/MS TNT; PETN; RDX 5 fg; 250 pg; 5 ng Evans et al. 2002
DART nitroaromatics 2 g/ml Song et al., 2009
LC-ESI RDX 2*10-8 M Sigman et al., 2005
APCI-CFI; quadrupole TNT, RDX 10-20 ppt; 0.3 ppt Takada et al., 2002
DESI RDX 0.5 ng Cotte-Rodriguez & Cooks 2006
Detection limits are very low for mass spectrometry methodes
Source: ON SPECTROMETRIC DETECTION TECHNOLOGIES FOR ULTRA-TRACES OF EXPLOSIVES: A REVIEWMarko Makinen, Marjaana Nousiainen, and Mika Sillanpaa
Limits of detection
Raman EffectInelastic scattering at vibrational modes
change in polarizability distinct signatures = selectivity low efficiency P10-7
pulsed lasers UV higher QE (resonances) SERS
Raman Spectroscopy
Moore, Scharff 2008
Experimental SetupMeasuring the frequency-shift q=is portable solutions stand-off detection
Raman SpectroscopySamples for Raman
fingerprints, fingernails pure explosives
aquaeous solutions vapour for SERS
detectable through various window materialonly little preparation
Sajanlal, Pradeep 2012
Advantages
selectivity sample preparation speed stand-off detection portable solutions
Disadvantages
(sensitivity) SERS ignition and eye-safety (Lasers) background elimination difficult in post-explosion analysis
Raman Spectroscopy
Raman stand-off PETN, RDX (>20m)TNT, UN (30m)DNT, TNT, RDX (7m)
IR SpectrumAbsorption at vibrational modes
change in dipol moment whole molecule (below 1300cm-1) functional groups (above 1500cm-1)
X-NO2 (vs, vas)
IR SpectroscopyBeveridge 2012 functional group symmetric vs asymmetric vas
C-NO2 1320-1390 cm-1 1510-1590 cm-1
Ring-NO2 1340-1370 cm-1 1520-1560 cm-1
C-O-NO2 1270-1285 cm-1 1640-1660 cm-1
N-NO2 1270-1310 cm-1 1530-1590 cm-1
http://www.sesame.org.jo
Experimental SetupMeasuring absorption in transmission or reflectance FTIR (interferometer) portable solutions stand-off detection
IR Spectroscopy
Advantages
selectivity stand-off detection portable solutions characteristic for functional
groups/inorganic atoms
Disadvantages
ignition absorption by air/water difficult in post-explosion analysis IR spectra sometimes similar low sensitivity (typical LOD 1mg)
Samples for IR pure explosives
gases/solids betwen plates, pellets aquaeous solutions
compounds are difficultchromatography (MS better)
reaction products after explosion e.g. carbonates, thiocyanates
US8222604 B2
Triacetone triperoxide (TATP)Combustible dust
Other explosives
There are other explosives out there that do not fit in the two categories shown before!
So, what happens in these cases?
Others - Organic Peroxides
Triacetone triperoxide, TATP
Primary explosive; Highly volatile, susceptible to heat, shock, or friction
Terrorists favorite explosive
Lack of Nitro groups
Home-made explosive:
July 2005 London bombingswww.globalresearch.ca
TATP traces detection in post-explosion debris by HS-GC/MS
Volatile compounds are separated according to their partitioning behaviour between mobile gas and stationary phase in the column. Identification of the analyte happens at the mass spectrometer detector
Unlikely that 2 different molecules behave similar in both techniques.
Transfer line
MSIonization, detection
Headspace Gas chromatography/ mass spectrometry (HS-GC/MS)
GCInjection,
separation
wikipedia.org
Headspace sampling:analysis of the gas phase in the headspace above the sample.
Post-explosion debris (soil, glass and metals) collected from the area of explosion in a glass container and heated. Then, a sample from the headspace is injected to GC/MS.
m/z [M-1]
Detection limit of 1 nanogram
TATP traces detection in post-explosion debris by HS-GC/MS