Lecture 4 Flashcards
What is the issue with clandestine explosives?
- Very dangerous
- Uncontrolled manufacturer
- Minimal temperature control
- No quality control
- Impure profiles which increase shock sensitivity
What has been done to prevent the manufacturing of clandestine explosives?
There have been regulations on the quantities of materials you can buy
what is a common clandestine explosive?
Acetone peroxide
What are the two different forms of of acetone peroxide?
- Dimer = DATP
- Trimer = TATP which is one of the most commonly used explosives
What is the problem with TATP?
It is so oxygen deficient it can’t even form CO and H2O without oxygen from the environment
How does TATP overcome it’s issue?
- The products do not conform to the K-W rules at all
- It is an endothermic reaction so it gets colder during the explosive reaction and takes heat in from the surroundings when its detonating
- It’s an entropic explosive and you can’t define the explosive power
- The products reform acetone and ozone which is very unusual
- There’s a positive enthalpy
Why is TATP often used?
- It generates a decent amount of gas but not hyde
- It doesn’t generate fire or sound when it explodes
- The materials are readily available
What is the problem with detecting TATP?
- It doesn’t have strong UV or visible absorption so HPLC and UV-Vis isn’t possible
- GC-MS is possible but is challenging as the sample isn’t pure and you can’t take this instrument to the scene of explosion
- It’s pretty volatile and challenging in the way it decomposes
What method is used to detect TATP?
Peroxidase enzyme
How do you perform the hydrogen peroxide test?
- Shine a 4nm UV light at the sample so it decomposes back into its starting reagents
- Add hydrogen peroxide
- If it turns from colourless to green then there is a chance you started with TATP
What is the problem with using the peroxidase enzyme test?
It isn’t very sensitive if you only have trace amounts
What was TATP used for?
Suicide bombings and explosives since 1980’s
What can low-quality materials lead to?
- Fizzled explosives
- TATP is not an ideal explosive in terms of it’s efficiency so it often fizzles out
What happens to explosives if they get wet?
The explosive material isn’t able to be packed as effectively
What does fuel generally need to contain?
Carbon
What effect does surface area have on the power of an explosive?
A higher surface area will make a more powerful exploive
What is ANFO?
- A fertiliser bomb
- It is made from ammonium nitrate and fuel oil
- Sometimes aluminium is added to increase the length of the blast
- Fertiliser and crude oil are readily available
What is “Annie”?
- ANFO combined with nitrobenzene
- It is used by the IRA in the 1980’s to 1990’s
What are explosive mixtures often based on?
The materials that are obtainable
What are taggants?
Taggants are additives that provide a traceable ‘signature’ to the explosive
What is the purpose of taggants?
- Used to deal with the illicit use of military or industrial grade plastic explosives
- Preventative and diagnostic
What properties do we want for taggants?
- Volatile so we can detect them in the gas phase
- Not used in other applications
- Chemically related in some way to the explosive it’s going to be used in
How can taggants be detected?
- They have a protein meaning you can easily detect them and trace them back to where they came from
- They’re volatile so they can be detected in the gas phase
- You may be able to find the recondensed forms of these
- They are chemically related to the explosive which gives a traceable signature
Why are pre-detonation taggants used?
- They are used in high security settings to prevent attacks
- They are typically detonated by sniffer dogs or mass spectrometry-based system
What order of magnitude is desired to detect trace amounts of explosives/taggants?
PPB
How does Ion Mobility Spectrometry work?
- Molecules are ionised by an electric field
- Resulting ions are fired through a tube against the action of a drift gas
What is the advantage of Ion Mobility Spectrometry?
- Faster separation of components compared to GC or LC
- It only takes milliseconds so it can rapidly analyse lots of samples
What is Ion Mobility often paired with?
A mass spectrometer usually TOF or Quadrupole-MS
What is the purpose of the drift gas in Ion Mobility Spectrometry?
It’s an inert gas, typically Argon, to prevent the reaction going off.
How does Ion Mobility Spectrometry achieve separation?
- Generate cations that enter the drift cube
- The electric field accelerates molecules from left to right.
- At the same time a drift gas is pumped in that goes in the opposite direction to the electric field.
- This prevents the molecules from going through really quickly.
- This affects the larger molecules more than the smaller ones so we get good separation
- The system will flag up anything that isn’t supposed to be there.
What affects ion mobility?
- Mass of ion
- Density of the drift gas
- Charge on the ion
What is gun cotton?
- Cellulose treated with nitric acid
- This is dangerous as it’s very difficult to remove the oxygen once it starts going
- Rapidly deflagrates
