Analytical strategy

Siiri BienzAdrian Woenkhaus Alvarez

Maya Amacha 03.12.2019

Explosives

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▪ Tang Dynasty in the 9th century invented gunpowder (coal, saltpeter, and sulfur)

▪ Nitroglycerin, developed in 1847▪ Nitrocellulose, trinitrotoluene (TNT) in 1863▪ Dynamite in 1867▪ Nowadays: C-4, RDX and PETN

The History of Explosives

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▪ Rapid decomposition into gas▪ 3 types: organic, inorganic and “dirty” explosives▪ Many different explosives -> mostly N/O compounds

General: Explosives

3TNT - 2,4,6-trinitrotoluene

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Common Explosives

Nitroglycerine Nitrocellulose

Perchlorate Pentaerythritol tetranitrate (PETN)

Mannitol hexanitrate

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Cyclotrimethylenetrinitramine (RDX)

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Type of attack Percentage (%)Assassination 8Facility/Infrastructure 8Hostage taking 8Armed assault 23Bombing/Explosion 52

Bombings

https://www.state.gov/j/ct/rls/crt/2015/257526.htm

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▪ amount stolen vs amount detonated▪ Identification of bomber▪ quality of the bomb▪ ratio of explosives

▪ Smuggling▪ dirty bombs -> amount of U/Po used

Quantitative approach

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Gathering evidences

Where How Collect

Gathering evidences

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Where to find evidences?

x y

x = Distance from epicenter to the most cdistant piece of evidence

y = 1.5 the distance x

Outer Perimeter

Inner Perimeter

Scene perimeterInvestigations from inner perimeter working toward the target

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Three general area at the explosions scene to find evidences:

-the target:-crater-witness material-area around crater

-the victims-outside the immidiate scence

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How to find evidences?

Detection by DogsDetection by Colorimetric methods

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Detection by DogsCan detect:

1) Explosive itself2) a contaminant or minor constituent of the explosive common to most batches

of that explosive 3) a decomposition product of that explosive

Sensitivity: Laboratory experiments 500 ppt – 10 ppb

Specifity: extremely good

Dynamic range: „tracking-to-source“

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Detection by Dogs

Advantages:− High sensitivity− High specifity− Portable

Disadvantages:− Generalization induces training

with variants of the target molecules

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Colorimetric method

Colometric Detection

Field

Evidence check

Combination with TLC

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An example: Nitroaromatic explosives (e.g. TNT)

Advantages:− Simple and inexpensive equipment− Sensitivity− Initial diagnostic test

Disadvantages:• Low specifity• Preferably an additional technique

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Test kit: TraceX™

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1) Documentation1) Log book2) Photographs3) Drawings

2) No Contamination

3) The correct container for the evidences -> Attention to volatile products

4) Proper labelling the different container

How to collect evidences?

Metal can Unconsumed high and low explosivesNylon zip-top Materials requiring explosives residues

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1) Log-book

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3) Correct Container

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4) Proper Labelling

− Case number − Address of the scene − Location of evidence found (grid) − Finder’s name and signature/initials − Short description − Item number − Evidence custodian’s name and

signature/initials who placed the item number on the container

− Date collected − Time found

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Overview of different analytical methods

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General examination sequence

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Sample preparation and Analysis

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Standard reference materials are essential for calibration and validation

Standard reference explosives are required to facilitate identification by direct comparison.

The main kit components are cotton swabs, forceps, gloves, solvent, self-seal plastic bags, and glass sample vials

Vacuum sampling involves drawing air over the surface of the item to be sampled using a vacuum pump and a modified glass tube holding filters for the collection of particulates.

This method of recovery is particularly effective on surfaces not suitable for swabbing such as fibrous materials and solvent-sensitive surfaces.

Sample preparation and Analysis-Solid Phase Extraction

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Gas Chromatography/Liquid chromatography with Mass Spectrometry

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MS serves as a detector for the gas and liquid chromatographic system

Low limit of detection: 0.18-1.11 ng for NICI

Ionization methods: ESI, APCI

Identification through fragmentation

Gas Chromatography with Chemiluminescence Detection (GC-ETA)

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Advantages

Highly selectiveeasy-to-use, robust, and sensitive Relatively cheap compared to other GC and LC techniques

DisadvantagesSome non-nitro containing explosives might not be detectedLarge to be used in field

Ozone Induced chemiluminescence

High temperature oxidative combustion

Ion Mobility Spectroscopy

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Ion Mobility Spectroscopy

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Advantages

- Operates at ambient pressure

- Relatively easy to use

- Portable

- Inexpensive

- Selective, sensitive (ppt)

Disadvantages

- Direct sampling is not possible

- Pre-conecentrators are greater in size than the IMS analyzer

- Not suitable for non volatile compounds

Ion Chromatography

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Easy to use

Fast detection method

Inappropriate for late eluting peaks such as perchlorate, carbonate, and thiocyanate.

Requires peak confirmation

Advantages

Disadvantages

Capillary Electrophoresis

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General function is similar: separation according to charge and sizeMany anions do not absorb in the UV, detection occurs by monitoring the loss In absorbance of the dichromate eluent at 280 nmMinimum detectable concentration is 0.5 ppm compared to IC which is 2 ppm

XRF

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Simple

Non-destructive

Requires little or no sample preparation

Surface analysis after explosions

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FTIR/RAMAN Spectroscopy

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FTIR/RAMAN Spectroscopy

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▪ Monoclonal antibodies produced for explosives▪ Upon binding -> change in fluorescence or optical

transmittance▪ Very low LOD▪ BUT timely -> Not for real time detection (e.g. airports)

Immunosensors

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Amplifying fluorescence polymers AFP

n n

h𝜈 h𝜈h𝜈‘

Principle: Fluorescence Quenching with explosive analyte

Amplification: only one explosive can quenched whole polymer

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Amplifying fluorescence polymers AFP

Advantages:− High sensitivity− Vapor phase detection− Portable devices

Disadvantages:− Explosives need to have certain

reduction potential

LOD = ppq

FIDO X4

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Electrochemical detection

-Potential of the electrode at a fixed value and measured the current as a function of time-Potential drive an electron process: reduction or oxidation-current: reflects rate of electron movement

-Nitrogroup -NO2 good electron acceptor and form amine-Peroxide explosives photochemical conversion to H2O2

-A promising research field: Lab-on-a-chip detection of explosives a) DNB

b) DNT

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Electrochemical detection

Advantages:− High sensitivity− Inherent miniaturization− Low power and cost requirements

Disadvantages:− Analyst need certain potential− Contamination problems

LOD = 100 pg

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Thin layer chromtatography TLC

Advantages:− Simplicity− Low material demand− Accurate seperation− Low power requirements

Disadvantages:− Only target analysis− Same Rf

Std. 1 Std. 2

TNT

RDX

Picric acid

HMX

Tertyl

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Bulk vs. trace analysis

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- Looks for a mass with certain properties considered indicative of an explosive

- High nitrogen and/or oxygen content and high bulk density are the properties usually targeted

- High probability for false negative or false positive

- Does not require libraries

Conclusion

There exists a wide variety of techniques to identify explosives

The sampling procedure is not easy and requires a lot of training and experience

Advances are towards developing portable analytical machines that can identify more detailed characteristics of the sample at hand

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▪ Hargis PJJr . 1997. Opt. Soc. Am. Annu. Meet., Long Beach, CA, p. 125

▪ Mercado A, Janni J, Gilbert B, Steinfeld JI. 1996. See Ref. 21, pp. 91– 99

▪ Spiro TG, Stein P. 1977. Annu. Rev. Phys. Chem. 28: 501– 21

▪ Janni J, Gilbert BD, Field RW, Steinfeld JI. 1997. Spectrochim. Acta 53A: 1375– 81

▪ Bart JC, Judd LL, Hoffman KE, Wilkins AM, Kusterbeck AW. 1997. Environ. Sci. Technol. 31: 1505– 11

Sources

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▪ R.L. Woodfin, 2007, Trace Chemical Sensing of Explosives, John Wiley & Sons Inc., Hoboken NJ

▪ J.T. Thurman, 2006, Practical Bomb Scene Investigation, CRC Press, Boca Raton FL

▪ A. Beveridge , Ed., Taylor & Francis Ltd, 2012, Forensic Investigation of Explosions, CRC Press, Boca Raton FL

▪ Xiancheng Sun, Ying Wang, Yu Lei, Chem. Soc. Rev., 2015, 44, 8019

▪ Morphix Technologies TraceX Explosives Detection Kit

Sources

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