Forensic Chemistry

Topics: Explosive material, Nitrogen, Improvised explosive device Pages: 8 (2272 words) Published: April 11, 2012
Forensic Chemistry
Home Made Explosive Investigation
Forensic examinations of bomb site are becoming more and more widespread and many analytical techniques are used. This report aims to show how a soil sample from the scene of a suspected homemade bomb factory was analysed using thin layer chromatography. This technique, although superseded by more modern techniques, still has an important part to play in any forensic investigation and will often be the first technique used by investigators to show that explosive materials are present. Introduction

This report aims to discuss explosives and the role they play in forensic investigations. A scenario was presented where a sample of material debris had been recovered from the scene of an explosion and need examined via aqueous and organic extraction techniques to identify the components. So what is an explosive? The legal definition under the United Kingdom’s 1875 Explosives Act, Section 3 states: ‘The term “explosive” in this Act-

1. Means gunpowder, nitro-glycerine, dynamite, guncotton, blasting powders, fulminate of mercury or of other metals, coloured fires, and every other substance, whether similar to those above mentioned or not, used or manufactured with a view to produce a practical effect by explosion or a pyrotechnic effect; and 2. Includes fog-signals, fireworks, fuses, rockets, percussion caps, detonators, cartridges, ammunition of all descriptions, and every adaptation or preparation of an explosive s above defined (White, 2009)

Putting that in simpler terms an explosive is defined as any material or device which, by the rapid release of its potential energy, is capable of producing an explosion. There are three main types of explosives: * Mechanical

* Nuclear
* Chemical
Explosives are further classified as low velocity and high velocity. Low explosives are classed as deflagrating explosives that will only detonate when confined. The detonation of a low explosive is usually used in order to detonate a high explosive which is not as sensitive (Bell, 2006).

The method for extraction in this practical was Thin Layer Chromatography (TLC). TLC is a quick and easy technique that is used to separate chemical compounds based on the rate at which they move through a mobile phase. TLC is generally used to check the purity of the product of a chemical reaction (Lewis and Evans, 2001) but can also be used to check the identity of an unknown sample. It is a qualitative test so it shows what is present but cannot show how much is present. Aims

The aims of this practical were to attempt aqueous and organic extractions of the debris and to identify any components present by a range of chromatographic techniques.

A sample of material debris recovered from the scene of an explosion was provided. The police suspect that the incident may have been an accidental detonation in a home laboratory.

The first part of the practical required an organic extraction of the material debris. Organic extraction uses a solvent which can extract any residual organic components, such as 2,4,6 – Trinitrotoluene (TNT); 1,3,5–Trinitro–1,3,5,-Triazacyclohexane (RDX); Pentaerythritol Tetra nitrate (PETN); Nitro-glycerine (NG) and other organic nitrogen compounds that may be present in explosive mixtures including propellants.

In order to carry out this part of the practical a sintered glass crucible of porosity 3 was obtained and weighed to 3 decimal places. Approximately 2.5g of the explosion scene residue was then added to the crucible and this was then weighed once more. The organic extraction could then be carried out by placing the crucible onto a vacuum pump and adding 10cm3 of toluene. The vacuum pump was then switched on to filtrate. The toluene was reused 3 times to make sure all the organic extract was washed through completely. The extract was collected into a stoppered flask and the crucible with the filtered soil sample...
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