Forensic analysis of explosives
Youngeun Choi, Dario Remmler, Maximilian Ries, Felix Rösicke, Radwan Sarhan, Felix Stete, Zhiyang Zhang Detecting and identifying explosives is of great importance
●Airport and airline security
●Demining Picture: Wo st 01/Wikipedia
●Removal of unexploded ordnance Picture: MatthiasKabel/Wikipedia
●Forensic analysis 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- Others: moieties:
K++ + S + C
Black powder
Trinitrotoluene (TNT) Triacetone triperoxide (TATP)
Dust of flammable materials
Ammonium nitrate Nitroglycerin (NG) Inorganic Explosives
Pure compounds
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
Ignition needed! Inorganic Explosives
Pure compounds Mixtures
Type Composition Characteristic ions
− + + ANFO NH4NO3, fuel oil NO3 , NH4 , MeNH3 (Ammonium nitrate fuel oil) (long chain hydrocarbons)
− 2- 2− Black powder Nitrates, sulfur, charcoal NO3 , SO4 , S2O3
fuel Na+, K+ /
salt - - Chlorate blends Chlorates, reducing agent ClO3 , Cl , (Metal powders, sugars etc.) Al3+, Na+, K+
Oxidizing - - Perchlorate blends Perchlorates, reducing agent ClO4 , Cl , (Metal powders, sugars etc.) Al3+, Na+, K+ 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) https://de.wikipedia.org/wiki/Ringprobe - – Brown ring reaction: NO3 – Berthelot reaction: NH + 4 Hubalek et al. 2007 • Flame colouring http://www.chemische-experimente.com/Alkalimetalle.htm
Reaction Ion LOD Source
- Brown ring NO3 30 μg/ml Stevens 1966
+ Berthelot reaction NH4 10 ng/ml Tsuboi et al. 2002 Inorganic Explosives
Off-site analytics Source: Forbes et al. 2014 • 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
Techniqueions can be preducedIon and detectedLOD more selectivelySource
– includes mappingAl3+ possibilities0.95 ng/l Gibson et al. 1991 - IEC ClO3 2 ng/ml Binghui et al. 2006 – high instrumental- effort ClO4 0.77 ng/ml Tian et al. 2003
K+ 10 ng DEFFI-MS Pb+ 1 ng Forbes et al. 2014 - ClO3 300 pg Nitro compounds
Explosives with nitro-groups: Violent decomposition of TNT:
2 C7H5N3O6(s) 12 CO(g) + 5 H2(g) + 3 N2(g) +2 C(s)
R.E. Factor: Relates an explosive´s demolition power to that of TNT
Trinitrotoluene (TNT) Relative to 1 kg TNT TNT 1
Black powder 0,55
Dynamite 1,54
RDX 1,60
Nitroglycerin (NG) Octanitrocubane 2,38
Nuclear bomb (Nagasaki) 4500 Mass Spectrometry exibits extraordinary properties in explosive detection
Mass Spectrometry Detection Limits
Modes 2,4,6-trinitrotoluene (TNT)* 3 pg/L Quadrupole Iontrap 2,4-dinitrotoluene (DNT)* 90 ng/L Time-of-flight (TOF) Tandem based (MS/MS) 1,3,5-trinitro-1,3,5-triazacyclohexane* 1 ng PETN** 1 ng
Ionization Matrix-assisted laser desorption/ionization Source: * Current trends in explosive detection techniques J. Sarah Caygill, Frank Electrospray ionization Davis, Seamus P.J. Higson
Chemical ionization ** 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 for examining surfaces
Direct Analysis in Real Time (DART)
Sample
Mechanism in Detail: Penning Ionization
M*+ S S+• + M + e- 3 +• 1 He(2 S) + H2O H2O + He(1 S) + electron + H2O+•+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. Laramée, J. Michael Nilles, H. Dupont Durst Atmospheric-pressure chemical ionization uses high temperatures for sampling
Atmospheric pressure chemical ionization interface (APCI)
Advantages: Disadvantage:
- soft ionization method - sample has to be in solution - reduces the thermal decomposition - possible to use a nonpolar solvent
Source: https://en.wikipedia.org/wiki/Atmospheric-pressure_chemical_ionization Detection limits are very low for mass spectrometry methodes
Limits of detection
ESI/quadrupole HMX;RDX;PETN;Tertyl 170 fmol/μL Straub & Voyksner, 1993
APCI;MS/MS TNT; PETN; RDX 5 fg; 250 pg; 5 ng Evans et al. 2002
DART nitroaromatics 2 μg/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
Source: ON SPECTROMETRIC DETECTION TECHNOLOGIES FOR ULTRA-TRACES OF EXPLOSIVES: A REVIEW Marko Ma¨kinen, Marjaana Nousiainen, and Mika Sillanpa¨a¨ Raman Spectroscopy
Raman Effect Inelastic scattering at vibrational modes • change in polarizability • distinct signatures = selectivity • low efficiency P≈10-7 – pulsed lasers – UV higher QE (resonances) – SERS
Experimental Setup
Measuring the frequency-shift ωq=ωi±ωs • portable solutions • stand-off detection Moore, Scharff 2008 Raman Spectroscopy Samples for Raman Sajanlal, Pradeep 2012 • fingerprints, fingernails • pure explosives – aquaeous solutions – vapour for SERS detectable through various window material only little preparation
Advantages Disadvantages
● selectivity ● (sensitivity) → SERS ● sample preparation ● ignition and eye-safety (Lasers) ● speed ● background elimination ● stand-off detection ● difficult in post-explosion analysis ● portable solutions Raman Spectroscopy
Limits of detection
Raman stand-off PETN, RDX (>20m) <20μg/mm-2 Moros et al. 2013 TNT, UN (30m) <500μg Gaft, Nagli 2008 DNT, TNT, RDX (7m) <3mg Pacheco-Londoño et al. (2009)
Portable 23 incl. TNT, DNT, RDX pure, mg Lewis 2005
SERS on vapour TNT 5 ppb Sylvia et al. 2000
SERS on liquids TNT, DNT 0,1 ppt Ko et al. 2009 TNT, DNT, DPA, RDX 10-7 M Sajanlal, Pradeep 2012 IR Spectroscopy
Beveridge 2012 functional group symmetric v asymmetric v IR Spectrum s as C-NO 1320-1390 cm-1 1510-1590 cm-1 Absorption at vibrational modes 2 -1 -1 • change in dipol moment Ring-NO2 1340-1370 cm 1520-1560 cm -1 -1 -1 • whole molecule (below 1300cm ) C-O-NO2 1270-1285 cm 1640-1660 cm -1 • functional groups (above 1500cm ) -1 -1 N-NO2 1270-1310 cm 1530-1590 cm – X-NO2 (vs, vas)
Experimental Setup Measuring absorption in transmission or reflectance • FTIR (interferometer) • portable solutions
• stand-off detection http://www.sesame.org.jo IR Spectroscopy
Samples for IR US8222604 B2 • pure explosives – gases/solids betwen plates, pellets – aquaeous solutions • compounds are difficult chromatography (MS better) • reaction products after explosion – e.g. carbonates, thiocyanates
Advantages Disadvantages
● selectivity ● ignition ● stand-off detection ● absorption by air/water ● portable solutions ● difficult in post-explosion analysis ● characteristic for functional ● IR spectra sometimes similar groups/inorganic atoms ● low sensitivity (typical LOD ≥ 1mg) Other explosives
There are other explosives out there that do not fit in the two categories shown before!
Triacetone triperoxide (TATP) Combustible dust
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 bombings
www.globalresearch.ca TATP traces detection in post-explosion debris by HS-GC/MS
Headspace Gas chromatography/ mass spectrometry (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
GC MS Transfer Injection, Ionization, line separation detection
Unlikely that 2 different molecules behave similar in both techniques. wikipedia.org TATP traces detection in post-explosion debris by HS-GC/MS
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. http://www.labhut.com/
Detection limit of 1 nanogram
Stambouli A. et al., Forensic Sci m/z [M-1] Int., 2004, 146S, S191 Immunosensor for TATP detection
Immunoassay: Biochemical test based on antibody/antigen interaction for qualitative and quantitative analysis.
Analyte, antibody and a detectable label
TATP immunogen TATP Hapten- BSA conjugate
M. Walter, U. Panne, M. Weller, Biosensors, 2001, 1, 93 http://www.invitro-test.com/ Sensitivity and selectivity of TATP antibody
Detection limit in the range of ng/L
No cross reactivities with other explosives
M. Walter, U. Panne, M. Weller, Biosensors, 2001, 1, 93 Others - Dust explosions
Dust explosions ; explosive combustion of dust cloud If particle size is less than 500 μm and suspended in air, the combustion rate is very fast and the energy required for ignition very small → Violent combustion! U.S. Chemical Saftey and Hazard Invesitagion Board (CSB)
Parnell, C. et al., J. Loss. Prevent. Proc. 2013, 26, 427 ASTM test methods: well-dispersed dust cloud is formed in a 20 L chamber, nearly spherical in shape, and subjected to a strong pyrotechnic ignition souce. Resulting pressure and rate of pressure rise are measured. Summary
Method Vibrational Mass Spectroscopy Others Sample condition Spectrometry Compound Solid (surfaces) Inorganic Salts/ DEFFI Colorimetric reactions Mixtures Liquid (dissolved)
Nitrogen containing Immunoassays and other Gaseous DART SERS/IR compounds techniques all phases Peroxides GC/MS Immunoassays
Sensitivity! Remote/ Instant on-site nondestructive! analysis!