Forensic analysis of explosives

Youngeun Choi, Dario Remmler, Maximilian Ries, Felix Rösicke, 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

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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 μg/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 explosive´s 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. Laramée, 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/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

Detection limits are very low for mass spectrometry methodes

Source: ON SPECTROMETRIC DETECTION TECHNOLOGIES FOR ULTRA-TRACES OF EXPLOSIVES: A REVIEWMarko Ma¨kinen, Marjaana Nousiainen, and Mika Sillanpa¨a¨

Limits of detection

Raman EffectInelastic scattering at vibrational modes

• change in polarizability• distinct signatures = selectivity• low efficiency P≈10-7

– pulsed lasers– UV higher QE (resonances)– SERS

Raman Spectroscopy

Moore, Scharff 2008

Experimental SetupMeasuring the frequency-shift ωq=ωi±ωs• 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

Stambouli A. et al., Forensic Sci Int., 2004, 146S, S191

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Immunosensor for TATP detection

Immunoassay:Biochemical test based on antibody/antigen interaction for qualitative and quantitative analysis.

Analyte, antibody and a detectable label

TATPimmunogenTATP Hapten-BSA conjugate

M. Walter, U. Panne, M. Weller, Biosensors, 2001, 1, 93 http://www.invitro-test.com/

Sensitivity and selectivity of TATP antibody

No cross reactivities with other explosives

M. Walter, U. Panne, M. Weller, Biosensors, 2001, 1, 93

Detection limit in the range of ng/L

Others - Dust explosionsDust explosions ; explosive combustion of dust cloudIf 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!

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.

U.S. Chemical Saftey and HazardInvesitagion Board (CSB)

Parnell, C. et al., J. Loss. Prevent. Proc. 2013, 26, 427

Summary

Method

Compound

Mass Spectrometry

Vibrational Spectroscopy Others

Inorganic Salts/Mixtures DEFFI

SERS/IR

Colorimetric reactions

Nitrogen containing compounds DART

Immunoassays and other techniques

Peroxides GC/MS Immunoassays

Sample condition

Solid (surfaces)

Liquid (dissolved)

Gaseous

all phases

Sensitivity! Remote/ nondestructive!

Instant on-siteanalysis!

Forensic analysis of explosivesFoliennummer 2Foliennummer 3Foliennummer 4Foliennummer 5Foliennummer 6Foliennummer 7Foliennummer 8Foliennummer 9Foliennummer 10Foliennummer 11Foliennummer 12Foliennummer 13Foliennummer 14Foliennummer 15Foliennummer 16Foliennummer 17Foliennummer 18Foliennummer 19Foliennummer 20Foliennummer 21Foliennummer 22Foliennummer 23Foliennummer 24Immunosensor for TATP detectionFoliennummer 26Foliennummer 27Foliennummer 28