Explosions 4 Flashcards
What are clandestine explosives?
Improvised explosive manufacturing
* Working in conditions that arent optimised
* Frequently used in terrorist attacks
* Manufacturing is usually uncontrolled and undertaken by a less experienced personnel
* No control of starting material impurity profile (can increase shock sensitivity)
* Often unaware of the exact product made
What is acetone peroxide?
- A common clandestine explosive
- Produced in both a dimer (DATP) and trimer (TATP)
- Very oxygen deficient - cant even form Co and H2O without O2 from environment
- Actual products dont conform with the K-W rules
- Forms acetone and ozone
The calculated heat of explosion is +10.8 kcal mol-1 for TATP, calculate the volume of detonation and say what this suggests about the explosion?
(produces 4 moles of gas)
V = 4 x 22.4 = 89.6 L mol-1
Entropic explosion - heat is taken in from the surroundings
Techniques you can and cant use and why
Detection of TATP
- No strong UV or visible absorption - HPLC/UV-vis not possible
- GC-MS possible but challenging due to it because volatile and not pure
Peroxidase enzyme: - Shine UV light, decomposes back into starting reagents
- Then test for hydrogen peroxide
- Colourless to green if possitive
- Not very sensitive
What are two other types of clandestine explosives other than TATP?
- ANFO = fertiliser bomb, ammonium nitrate and fuel oil
- ANFO + nitrobenzene
What are taggants?
Additivies that provide a traceable ‘signature’ to the explosive
What kind of quality would we want in an explosive taggant and why?
- Volatile = easily detected in the gas phase
- Not used in other application = no good for a taggent to be able to be found anywhere (wont know if its from the explosive or just found at the scene)
What are pre-detonation taggants used for and where?
Used to prevent attacks in high security settings - government buildings and airports
* Detected by sniffer dogs or MS systems
Why arent sniffer dogs the best for detecting taggants and what is better?
- Sniffer dogs can only smell up to ppm which might not be enough to identify them
- MS has a much higher sensitivity (ppb)
How does ion mobility spectrometry work?
- Molecules are ionised by an electric field to accelerate them
- Drift gas is pumped in a different direction - prevents molecules from passing through too quickly and larger molecules will be affected more = better separation
What are the advantages of an ion mobility spectrometer?
- Analysis time is short so not a long wait for samples to pass through - ideal for high security settings
- Faster separation than GC or LC (milliseconds)
- Automated software can flag any components that are suspicious
What factors can affect the ion mobility in an ion mobility spectrometer?
- Reduced mass of the ion
- Number density of drift gas (molecules/volume)
- Collisions cross section (probability of collision with drift gas)
- Charge on the ion
How are nitrocellulose-like materials made and why are they so dangerous?
- Cellulose treated with nitric acid
- Cellulose can be obtained from a sock
- Very difficult to remove the oxygen once deflagration has began so it will keep burning until all the products has been used up
