Lecture 4

Question 1

What is the issue with clandestine explosives?

Answer 1

• Very dangerous
• Uncontrolled manufacturer
• Minimal temperature control
• No quality control
• Impure profiles which increase shock sensitivity

Question 2

What has been done to prevent the manufacturing of clandestine explosives?

Answer 2

There have been regulations on the quantities of materials you can buy

Question 3

what is a common clandestine explosive?

Answer 3

Acetone peroxide

Question 4

What are the two different forms of of acetone peroxide?

Answer 4

• Dimer = DATP
• Trimer = TATP which is one of the most commonly used explosives

Question 5

What is the problem with TATP?

Answer 5

It is so oxygen deficient it can’t even form CO and H2O without oxygen from the environment

Question 6

How does TATP overcome it’s issue?

Answer 6

• 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

Question 7

Why is TATP often used?

Answer 7

• 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

Question 8

What is the problem with detecting TATP?

Answer 8

• 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

Question 9

What method is used to detect TATP?

Answer 9

Peroxidase enzyme

Question 10

How do you perform the hydrogen peroxide test?

Answer 10

• 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

Question 11

What is the problem with using the peroxidase enzyme test?

Answer 11

It isn’t very sensitive if you only have trace amounts

Question 12

What was TATP used for?

Answer 12

Suicide bombings and explosives since 1980’s

Question 13

What can low-quality materials lead to?

Answer 13

• Fizzled explosives
• TATP is not an ideal explosive in terms of it’s efficiency so it often fizzles out

Question 14

What happens to explosives if they get wet?

Answer 14

The explosive material isn’t able to be packed as effectively

Question 15

What does fuel generally need to contain?

Answer 15

Carbon

Question 16

What effect does surface area have on the power of an explosive?

Answer 16

A higher surface area will make a more powerful exploive

Question 17

What is ANFO?

Answer 17

• 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

Question 18

What is “Annie”?

Answer 18

• ANFO combined with nitrobenzene
• It is used by the IRA in the 1980’s to 1990’s

Question 19

What are explosive mixtures often based on?

Answer 19

The materials that are obtainable

Question 20

What are taggants?

Answer 20

Taggants are additives that provide a traceable ‘signature’ to the explosive

Question 21

What is the purpose of taggants?

Answer 21

• Used to deal with the illicit use of military or industrial grade plastic explosives
• Preventative and diagnostic

Question 22

What properties do we want for taggants?

Answer 22

• 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

Question 23

How can taggants be detected?

Answer 23

• 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

Question 24

Why are pre-detonation taggants used?

Answer 24

• They are used in high security settings to prevent attacks
• They are typically detonated by sniffer dogs or mass spectrometry-based system

Question 25

What order of magnitude is desired to detect trace amounts of explosives/taggants?

Answer 25

PPB

Question 26

How does Ion Mobility Spectrometry work?

Answer 26

• Molecules are ionised by an electric field
• Resulting ions are fired through a tube against the action of a drift gas

Question 27

What is the advantage of Ion Mobility Spectrometry?

Answer 27

• Faster separation of components compared to GC or LC
• It only takes milliseconds so it can rapidly analyse lots of samples

Question 28

What is Ion Mobility often paired with?

Answer 28

A mass spectrometer usually TOF or Quadrupole-MS

Question 29

What is the purpose of the drift gas in Ion Mobility Spectrometry?

Answer 29

It’s an inert gas, typically Argon, to prevent the reaction going off.

Question 30

How does Ion Mobility Spectrometry achieve separation?

Answer 30

• 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.

Question 31

What affects ion mobility?

Answer 31

• Mass of ion
• Density of the drift gas
• Charge on the ion

Question 32

What is gun cotton?

Answer 32

• Cellulose treated with nitric acid
• This is dangerous as it’s very difficult to remove the oxygen once it starts going
• Rapidly deflagrates