Explosions 7 Flashcards
How do we analyse explosives?
What is the device called?
Why can’t we use standard analytical techniques?
Using explosive-specific detection systems
Using the chemiluminescence of C-NO2, N-NO2, O-NO2 groups
Thermal energy analyser - controlled pyrolysis to form NO (Pyrolysis – thermal decomposition in absence of air)
They do not always provide sufficient evidence. Non-explosive compounds may have very similar molecular weights and retention times
Describe the reaction used by a TEA?
How is this used to detect explosive compounds?
Explosive compound undergoes pyrolysis to generate NO radical in excited state (NO*)
Nitrosyl radical (NO) is reacted with ozone to generate an excited nitrogen dioxide radical (NO2)
This decays to ground state (NO2* to NO2). This emits light around 600nm if NO2 group present.
If have other compounds of similar molecular weights that do not have NO2 groups these won’t emit light in this process.
What are the five advantages of TEA?
- picogram limit of detection (LOD)
- simple (easy to use (no training) and maintain)
- fast (10 minutes for run time when coupled to GC/LC)
- reliable
- robust evidence (no known false positives in decades of use)
How many columns are used in analysis? Name these.
How are these used?
BP1 - non polar
BPS - slightly polar
CPSIL19 - polar
If all three columns indicate presence of an explosive, the analysis is considered trustworthy
What else is added to TEA?
What are the three properties of this that is added?
Give two examples and explain how they fit property list.
Reference compounds
- must be well known compounds containing nitro functionalities
- need TEA positive response
- need to have different retention times to any explosives/taggants
2-fluoreo-5-nitrotoluene (fluorine so shifts RT)
Musk tibetene (butyl group so shifts RT)
What is the order in which protocol sets out analysis using a TEA?
- run standard of explosive (high purity) we are interested in (+internal standard)
- run blank sample (+internal standard) to make sure sample is clean and check for any impurities on column
- run sample (+internal standard)
- run standard again (+internal standard) to ensure haven’t got any shifts in RT
- calculate RRT% difference (relative retention time)
RRT= RT peak/RT reference
RRT% difference = (RRT sample - RRT standard) / RRT standard - apply acceptance criteria (confirm identity if %RT difference is less than 0.50%
- then run on other two columns
where internal standard = reference compound
How do you work out total mass of explosive?
Mass sample injected = mass standard injected x (peak area (sample) /peak area (standard))
Total mass = mass injected x (total volume of sample/volume injected)
What technique is good for analysis of non-UV active, non-nitro organic based explosives?
What is a disadvantage of this technique?
IR radiation techniques (FTIR and raman spectroscopy)
Bad for complex mixtures as spectra get very complicated so this technique must be used in combination with another technique.
What technique is good for analysis of explosives containing inorganic species?
What inorganic species can it detect?
What does it allow to be done?
What are advantages (2) and limitations (2)?
Give an alternative to this technique?
SEM-EDX
Inorganic fuels - Mg, S, Al
Inorganic oxidisers - KClO4, KNO3, NH4NO3
SEM - microscopy allows us to take images of sample and look at different positions and EDX - can give us elemental information
Advantages:
1. non-destructive (in reality hard to mount samples without destroying them)
2. area mapping - can observe sample inhomogeneity
Disadvantages:
1. only gives element and OS
2. not the highest sensitivity so limitation for trace analysis
XPS (X-ray photoelectron spectroscopy) - provides higher sensitivity but cannot be used for mapping
What are two techniques used to separate inorganic species?
Explain what they separate based on?
Can these techniques be used complementarily and what for?
Ion exchange chromatography separates ions based on charge (higher charge elutes more slowly)
Capillary electrophoresis uses electric field to separate ions based on size and charge
Yes, to get a clearer picture for definitely identifying and quantifying different relative complexes/inorganic species we might have
What technique do we use to detect fuels and accelerants (hydrocarbons)?
GC with flame ionisation detection (GC-FID)
What are the 2 purposes of explosives legislation?
When did these first come in explosives acts?
health and safety (control and safe use of legitimately held explosives) - 1875 EA
criminal activity (intent to cause harm) - 1883 EA
State the 4 offences in the 1883 Explosive Substances Act?
- causing an explosion likely to endanger life and property
- any act with intent to cause an explosion
- making or keeping explosives with intent to endanger
- making or keeping explosives under suspicious circumstances (vague
Why is explosive legislation different to a lot of legislation in UK?
The burden of proof is with the accused
If you are found to have explosive materials, it is up to you to prove/convince that you don’t intent to use it for illegal purposes e.g. intent to cause harm
What was a problem with the 1883 Explosive Substance Act?
What was done about this?
It didn’t define ‘explosive’
R vs Wheatley 1979 amended to give examples of explosives
