analysis of explosives - eth z · 2016-11-23 · advancesin analysis anddetectionofexplosives, j....
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|| 22.11.2016Analytical Strategy
Analytics of Explosives
Analytical Strategy, HS 16
Anne Schuhmacher, Caterina Bernasconi, Dario Schmid
Expert: Dr. K. Schlatter, Scientific Research Service (SRS)
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Table of contents
1. Introduction
• Where and what to detect?
• Explosion process
• Classification of explosives
2. Gathering Evidence
• Dogs
• Test kits (colorimetric methods)
• Flame coloration tests
||
3. Sampling and Sample Preparation
• Sampling
• Sample Preparation for Organic and Inorganic Compounds
4. Analytical Methods
• Organic explosives
• Inorganic explosives
5. Trace vs. Bulk Analysis
22.11.2016Analytical Strategy 2
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1. Introduction
Where to look for explosives?
• Airport security control
• Quality control in production
• Forensic examination
• Demining
||
What to detect in an explosion incident?
• Who is responsible for the explosion?
• What was the explosive?
• Where was the source of the explosion?
• How was the bomb built?
22.11.2016Analytical Strategy 3
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1. Introduction
Explosion process
Explosion
After ignition, decomposition, production of gas and heat as well as a fast expansion of matter is observed.
Deflagration
The expansion and decomposition take place at a speed slower than the speed of sound.
||
The expansion and decomposition take place at a speed slower than the speed of sound.
Detonation
The expansion and decomposition take place at a speed faster than the speed of sound.
22.11.2016Analytical Strategy 4
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1. Introduction
Classification:
• Organic explosives
Nitro compounds Peroxides
||
Nitroglycerin Trinitrotoluene (TNT) Hexogene Triacetonetriperoxide (TATP)
• Inorganic explosives
Salts Black powder: KNO3, S, C
Elemental sulfur
Red phosphoruschlorates perchlorates nitrates
22.11.2016Analytical Strategy 5
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2. Gathering Evidence
Trackhounds
Principle: Dogs can be trained on explosives in order to detect them at an explosion incident
Sensitivity: very good
• Laboratory experiments: 2,4-dinitrotoluene ≥ 500 ppt
nitroglycerin ≥ 10 ppb
Specificity: extremely good
• Laboratory experiments show very good discrimination of components
• Equilibrium between specificity and generalization needed
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• Equilibrium between specificity and generalization needed
Dynamic Range: „tracking-to-source“
Advantages:
• Very sensitive and specific
• Rather inexpensive
Drawbacks:
• No determination of the substance
• Skilled handler and dog necessary
22.11.2016Analytical Strategy 6Aspects of Explosives Detection, M. Marshall and J. C. Oxley, Ed., Elsevier, Oxford UK, 2009.
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2. Gathering Evidence
Test kits – colorimetric methods
Principle: The reaction of a specific explosive with a specific reagent leads to a color change indicating the
presence of the explosive.
Detection of nitroaromatic explosives, e.g. TNT
• Nitroaromatic compounds form coloured products in presence of alkalis
• Example: Janowski reaction
NO2
KOH (aq), acetone
NO2
||
Detection of nitrate esters, e.g. Nitrogycerol
• Detection based on detection of NO2
- ions formed during the reaction
• Example: Griess reaction
22.11.2016Analytical Strategy 7Aspects of Explosives Detection, M. Marshall and J. C. Oxley, Ed., Elsevier, Oxford UK, 2009.
O2N NO2
KOH (aq), acetone
NO2O2N
ONO2
R
H
OH+
- H2OR O + NO2
S
O
H2NO
NH2
+ NO2
NH
NH2
S
O
H2NO
N2
S
O
H2NO
NN
NH
NH2
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2. Gathering Evidence
Test kits – colorimetric methods
Detection of peroxide-based explosives, e.g. TATP
• Detection via enzymatic methods
• Example: Oxidation of ABTS
Detection limit for TATP: 8×10-6 mol/L
N
SO3S
N
NS
N
SO3
H2O2, peroxidase
N
SO3S
N
NS
N
SO3
||
Detection limit for TATP: 8×10-6 mol/L
Test Kits for Field Tests
• Field tests are carried out as preliminary examination
on the site of explosion
• Several kits based on the colorimetric tests for
different explosives
22.11.2016Analytical Strategy 8Aspects of Explosives Detection, M. Marshall and J. C. Oxley, Ed., Elsevier, Oxford UK, 2009.
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2. Gathering Evidence
Flame coloration test
Principle: Different cations lead to different coloration of the Bunsen burner flame.
Method gives an idea, if or which cations are in the sample.
Coloration:
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3. Sampling and Sample Preparation
Sampling
What are the samples?
• Explosion mostly leads to big destruction => sampling difficult
• Mostly: the intact explosive itself is not found
• Sampling of exploded material, e.g. the container of the bomb
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Important aspects while sampling
• Traces should not get lost
=> careful packaging and wiping of the sample
• Safety
22.11.2016Analytical Strategy 10Advances in Analysis and Detection of Explosives, J. Yinon, Ed., Kluwer Academic Publishers, Dordrecht, 1992.
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3. Sampling and Sample Preparation
Sample Preparation for Organic and Inorganic Compounds
Liquid Extraction
• Wipe containing organic and/or inorganic sample
• Extraction of the wipe with solvent ethanol/water
� organic as well as inorganic compounds recovered in good yield
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� organic as well as inorganic compounds recovered in good yield
• Extraction with organic solvent and pure water
� separation of organic and inorganic compounds
22.11.2016Analytical Strategy 11http://www.canberra.edu.au/researchrepository/file/b27875cd-8480-b507-d99e-09b23c4ff7ac/1/full_text.pdf, retrieved: 22/11/16
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3. Sampling and Sample Preparation
Sample Preparation for Organic Explosives
Supercritical fluid extraction
• Extraction of the explosive from a sample support, e.g. soil or wipe
• Principle:
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• Recovery of explosives good with ≥ 60% with pure CO2
22.11.2016Analytical Strategy 12Advances in Analysis and Detection of Explosives, J. Yinon, Ed., Kluwer Academic Publishers, Dordrecht, 1992.
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4. Analytical Methods
Methods for organic explosives
• GC/LC-MS
Spectrometers: Quadrupole and ion trap
Ionization methods: ESI, APCI
Identification through characteristic fragment ions
Advantages:
- can be miniaturized
||
- can be miniaturized
- sensitivity
- selectivity
- speed of the analysis
- LC-MS: analysis at room temperature
Drawbacks:
- Costs
- Complexicity
22.11.2016Analytical Strategy 13Aspects of Explosives Detection, M. Marshall and J. C. Oxley, Ed., Elsevier, Oxford UK, 2009.
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4. Analytical Methods
Methods for organic explosives
• GC-MS: Example
Mixture of explosives (10 ppb each)
Experimental:
- liquid-liquid extraction from H2O
- x100 concentration
- NICI
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- NICI
- Detection limits: 0.18-1.11 ng
22.11.2016Analytical Strategy 14Aspects of Explosives Detection, M. Marshall and J. C. Oxley, Ed., Elsevier, Oxford UK, 2009.
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4. Analytical Methods
Methods for organic explosives
• Ion Mobility Spectroscopy
How it works:
- Sampling with cloth strip
- Heating to 200°C
- Ionization
- Electric field: 200 V/cm
- Detector� electric signal
- Identification: characteristic ions
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- Identification: characteristic ions
Advantages:
- Low limits of detection (pg)
- High selectivity
- Ambient pressure
- Simple instrumentation & low maintenance
- Fast, Portable, Inexpensive
Disadvantages:
- Need for human work
Limits of detection: pg
22.11.2016Analytical Strategy 15Aspects of Explosives Detection, M. Marshall and J. C. Oxley, Ed., Elsevier, Oxford UK, 2009.
Trace Chemical Sensing of Explosives, John Wiley & Sons Inc., Hoboken NJ, 2007.
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4. Analytical Methods
Methods for organic explosives
• Ion Mobility Spectroscopy: more in detail
Sampling:
Difficulty: large air volumes as sample � preconcentration necessary:
air drawn through a metal mesh where the sample accumulate
Ion formation:
Reaction of the sample with a reservoir of ions
||
Ion sources:
- 10 mCi 63Ni
- ESI
- Electric discharge
- Photoinitiation
22.11.2016Analytical Strategy 16Aspects of Explosives Detection, M. Marshall and J. C. Oxley, Ed., Elsevier, Oxford UK, 2009.
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4. Analytical Methods
Methods for organic explosives
• Amplified Fluorescent Polymers
How it works:
- Introduction of sample in a conjugated polymer
- Fluorescence induced by irradiation with UV/Vis
- Analyte binds to a conjugated fluorescent polymer � Fluorescence Quenching (FQ)
- Photodetector: diminution of the emission intensitiy indicates that the analyte is present.
Explosives (TNT, DNT) very electron deficient (A): readily accept electrons from excited fluorophores (D)
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Explosives (TNT, DNT) very electron deficient (A): readily accept electrons from excited fluorophores (D)
Amplification of the signal:
Binding of a single analyte molecule quenches the fluorescence of the whole polymer.
22.11.2016Analytical Strategy 17Aspects of Explosives Detection, M. Marshall and J. C. Oxley, Ed., Elsevier, Oxford UK, 2009.
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4. Analytical Methods
Methods for organic explosives
• Amplified Fluorescent Polymers
Selectivity:
- Fluorescence quenching only efficient with favourable reduction potential: Ered
> - 1.52eV
- Vapor pressure can lead to different temporal responses
Thin-film conjugated polymers:
- Easier to use
||
- Easier to use
- No influence by solvatation or diffusion
- Even better amplification
- Problem: non-fluorescent aggregates have to be avoided
Advantages:
- Properties tunable through side groups
- High sensitivity
- Selectivity
Drawbacks:
Only explosives with a suitable reduction potential can be detected.
22.11.2016Analytical Strategy 18Aspects of Explosives Detection, M. Marshall and J. C. Oxley, Ed., Elsevier, Oxford UK, 2009.
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4. Analytical Methods
Methods for organic and inorganic explosives
• ED-XRF
- Irradiation of the sample with X-ray
� excitation of electrons in energetically low
lying orbitals (closed shells)
- Relaxation of electrons in higher lying
orbitals (valence shell)
� characteristic bands of the element
||
� characteristic bands of the element
- Application for surface analysis after explosions
- Exists as a portable device
22.11.2016Analytical Strategy 19https://www.911metallurgist.com/blog/portable-xrf-analyzer-price; retrieved: 22/11/16
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4. Analytical Methods
Methods for organic and inorganic explosives
• IR / Raman Spectroscopy
strong characteristic absorptions in the IR region
Example: R-NO2
:
- Diagnostic value: is there a nitro peak?
- λ depends on the type of atom to which the
nitro group is directly attached
- E.g. C-NO2: ν
as≈ 1590 – 1510 cm-1, ν
s≈ 1390 –
||
- E.g. C-NO2: ν
as≈ 1590 – 1510 cm-1, ν
s≈ 1390 –
1320 cm-1;
Analysis of mixtures:
- IR can identify the components
- Spectrum of a known component can be
artificially substracted
- Previous separation
Ambiguous identification:
Combination with retention data from
chromatographic methods
22.11.2016Analytical Strategy 20
IR spectrum of TNT
Forensic Investigation of Explosions, A. Beveridge, Ed., Taylor & Francis Ltd, CRC Press, Boca Raton FL, 2009.
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4. Analytical Methods
Methods for organic and inorganic explosives
• IR / Raman Spectroscopy
Advantages:
- Portable
- Easy to use, low maintenance
- non-destructive
- fast
- small amount of sample necessary & small sample preparation
||
Drawbacks:
- Less sensitive than MS (� IR not so suitable for trace analysis)
- IR: very sensitive to moisture
- Raman: Fluorescence
- NIR can burn dark substances
Limit of detection ≥ 1 mg
22.11.2016Analytical Strategy 21Forensic Investigation of Explosions, A. Beveridge, Ed., Taylor & Francis Ltd, CRC Press, Boca Raton FL, 2009.
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4. Analytical Methods
Differential Reflection Spectroscopy (DRS)
• Light source – UV (or visible or near infrared)
• Detection – reflectivity of the surface of the inspected area
• Each material has a unique electronic structure
• LOD: 10-7 g to 5×10-5 g depending on the
method/set-up parameters
Fingerprint for identification of substance
||
Fingerprint for identification of substance
Using curve discrimination programs.
Advantages:
• Contact-less
• Fast
• Differentiation between explosives
Drawbacks:
• Surface measurements only
The technique can be developed into a device
that is lightweight, rugged, and small.
22.11.2016Analytical Strategy 22T. Dubroca, G. Brown, R.E. Hummel, Optical Engineering 53(2), 021112 (February 2014)
Trace Chemical Sensing of Explosives, John Wiley & Sons Inc., Hoboken NJ, 2007.
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4. Analytical Methods
Methods for inorganic explosives
• General
Reminder: chlorates, nitrates, nitrites, …
Measurement assurance: Need positive results from two independent tests.
- Spot tests (e.g. Griess test for nitrite)
SH2N
ONH
NH2
SH2N
O S
O
H2NO
||
- Ion Chromatography (IC)
- Capillary Electrophoresis (CE)
- IR Spectroscopy
results of the spot tests or the infrared spectra can be inconclusive or unsatisfactory
� IC or CE useful
22.11.2016Analytical Strategy 23J. Yinon (ed.), Advances in Analysis and Detection of Explosives, 41-54. (1993)
S
O
NH2
+ NO2
HS
O
N2
O
NN
NH
NH2
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4. Analytical Methods
Methods for inorganic explosives
• Ion Chromatography
Ion separation:
- Nice for many anions (importantly chlorate from nitrate)
- Difficulties with late eluting peaks
- complex interactions of ions with stationary phase
||
- Need peak identity confirmation
(2nd measurement needed)
Detection:
- Conductivity of eluent suppressed by corresponding
acids of measured anions (modification by column)
- Linear dynamic range:
chlorate, nitrate 10 – 200 ppm
nitrite – 100 ppm
- Limit of Detection: ̴ 2 ppm
22.11.2016Analytical Strategy 24J. Yinon (ed.), Advances in Analysis and Detection of Explosives, 41-54. (1993)
J. Yinon (ed.), Advances in Analysis and Detection of Explosives, 133-144, (1993)
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4. Analytical Methods
Methods for inorganic explosives
• Capillary Electrophoresis
Ion separation:
- Nice for many anions
Plate number up to 70‘000 (vs. 3‘000 for IC)
- NO difficulties with late eluting peaks
- difference in charge to mass ratio of solvated ions
- Ion mobility: induced or electroosmotic flow
||
Inverse photometric detection:
- Anions cause loss in absorbance of the eluent
at certain wavelengths (e.g. 280 nm, dichromate)
- Linear dynamic range: 1 – 50 ppm
- Limit of Detection: ̴ 0.5 ppm
- Peak identity confirmation:
second analysis with detection at a
lower wavelength
22.11.2016Analytical Strategy 25J. Yinon (ed.), Advances in Analysis and Detection of Explosives, 133-144, (1993)
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4. Analytical Methods
Methods for inorganic explosives
• IC and CE – Complementary Methods
Excellent way to confirm peak identities:
- Differences in elution order � peak interferences easy to detect
Combine Advantages:
- High sensitivity (CE)
||
- High sensitivity (CE)
- Low limit of detection (CE)
- Wide concentration variety (IC)
- Broad analyte diversity (IC)
22.11.2016Analytical Strategy 26J. Yinon (ed.), Advances in Analysis and Detection of Explosives, 133-144, (1993)
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5. Trace vs. Bulk Analysis
Bulk analysis
Difference between trace and bulk analysis
• Trace analysis: look for a specific chemical from a library
• Bulk analysis: analysis of a property indicative for an explosive
Bulk analysis
• Adavantage: No limitation to a library of compounds
• Drawback: Less specific, more false results possible
||
• Drawback: Less specific, more false results possible
• Properties of explosives: high density, high oxygen- and/or nitrogen content, fast energy release
• Most important technique: X-ray analysis and X-ray computer tomatographic analysis
� analysis of density
� penetration of the sample with the x-ray smaller, the more dense the sample
• Sample can be extracted and diluted to proceed with the trace analysis procedures
22.11.2016Analytical Strategy 27Aspects of Explosives Detection, M. Marshall and J. C. Oxley, Ed., Elsevier, Oxford UK, 2009.
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6. Conclusion
• Diverse challenges in detection of explosives
• Broad variety of chemicals considered as explosive material
• Various methods for sample preparation and detection available
• Knowledge about the explosive can help to identify the criminals
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6. Conclusion
Thank you for your attention!
||
Thank you for your attention!
22.11.2016Analytical Strategy 29
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� Forensic Investigation of Explosions (Second Edition), A. Beveridge, Ed., Taylor &
Francis Ltd, CRC Press, Boca Raton FL, 2012.
� Aspects of Explosives Detection, M. Marshall and J. C. Oxley, Ed., Elsevier, Oxford
UK, 2009.
� R.L. Woodfin, Trace Chemical Sensing of Explosives, John Wiley & Sons Inc.,
Hoboken NJ, 2007.
Sources
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Hoboken NJ, 2007.
� J.T. Thurman, Practical Bomb Scene Investigation, CRC Press, Boca Raton FL, 2006.
� Advances in Analysis and Detection of Explosives, J. Yinon, Ed., Kluwer
Academic Publishers, Dordrecht, 1992.
22.11.2016Analytical Strategy