Lecture 7 Flashcards
How does a chemiluminescence detector work?
Different N groups have different chemiluminscence
Rewatch section on TEA ANALYSER
Lecture 7
What are the advantages of the TEA system?
- Picogram limit of detection (LOD)
- Simple 🡪 easy to use and maintain
- Fast
- Reliable
- Robust evidence
- No known false positives despite decades of use
What columns are used in TEA?
- BP1 (Non-Polar)
- BP2 (Slightly polar)
- CPSIL19 (Polar)
BP2 column
- Only very slightly polar
- Changing SP to have a small amount of phenyl groups instead of methyl
- Difference in polarity is enough to slightly shift retention times
CPSIL19 Column
- Not actually very polar but it’s more polar than the others
- Introduces small amount of phenyl groups and Si-CN groups
- Will increase the retention times if they are more polar
What is the importance of the 3 different columns in TEA?
- If all three indicate the presence of an explosive the analysis is considered trustworthy
- The same experiment is done 3 times using 3 columns of slightly different polarity
What are the reference compounds in TEA?
Reference compounds are well-known compounds containing nitro functionality
How does TEA work?
Different explosives and taggants have different retention times which are known
What does TEA detect?
Nitrogen-containing groups
What is the process for each column in TEA?
- Run a standard of the explosive we’re interested in + Internal Standard
- Run a blank + Internal Standard
- Run sample + Internal Standard
- Run a standard of the explosive we’re interested in + Internal Standard
- Calculate %RRT Difference
- Apply Acceptance Criterion
- Confirm on two other systems
BP1 Column
Non-polar column
How do you calculate Relative Retention Time (RRT)?
Look at retention time of the sample and divide by the retention time of the reference compound
How do you calculate % RT difference?
((RRT of Sample - RRT of standard) / RRT of Standard) x 100
What does the %RT difference tell us?
- How close is the sample retention time vs standard retention time
- This value gives us an idea about how confident that is it is the sample we believe it is
What should the difference be less than for %RT Difference?
The difference should be less than 0.50%
How do you calculate the mass of the sample injected?
Mass of sample injected = Mass of the standard injected x (Peak area of sample / Peak area of standard)
Total mass equation
Total mass = mass injected x (Total volume of sample / volume injected)
- Rewatch lecture to check values
What is the main technique used for explosive compounds containing nitrogen?
- TEA
- ADD TO THIS!
What are FTIR and Raman used for when investigating explosive compounds?
- They could be used to identify specific functional groups
within explosive compounds - Useful for non-UB active and non-nitrogen organic-based explosives
- Can detect the presence of TATP
- These methods are typically used in combination with other techniques
What is the drawback of using FTIR and Raman (IR radiation techniques)
- They are bad for complex mixtures as the spectra get messy and hard to interpret
- TEA is better for nitrogen-containing groups
- Not great for UV-active explosives
- Other methods exist to analyse inorganic techniques
What technique is useful for the analysis of inorganic explosive species?
SEM-EDX
What can SEM-EDX be used for?
- SEM-EX is widely used for inorganic species
- Inorganic fuels (Mg, S, Al)
- Inorganic oxidizers (KClO4, KNO3, NH4NO3)
- Microscopy allows us to take images of sample so we can look at different positions
- EDX can identify the chemical composition so we can identify the different elements present
What are the advantages of SEM-EDX?
- Non-destructive - in reality its hard to mount sample without damaging them but they can potentially be used again for repeat analysis
- Area mapping 🡪 can observe sample inhomogeneity
What are the limitations of SEM-EDX?
- Only gives element and oxidation state
- Not the highest sensitivity in comparison to other techniques which can be a limitation for trace analysis
- Doesn’t give usw an idea about where the other elements are coming from
What technique provides a higher sensitivity over SEM-EDX?
X-ray photoelectron spectroscopy (XPS) is an alternative technique that provides higher sensitivity but cannot be used for mapping
How can inorganic species be separated?
- Ion exchange liquid chromatography
- Capillary electrophoresis
- Using both techniques can be helpful for identifying and quantifying the different inorganic complexes and making sure we’ve identified the complexes correctly
Ion exchange liquid chromatography
- Used to separate inorganic species
- Higher charge elutes slower
- Separates based on the charge
- Can be used for more inorganic complexes
Capillary electrophoresis
- Separates inorganic species
- Electric field separates ions based on size and charge
- We get slightly different elution order with capillary electrophoresis
How can you detect fuels and accelerants?
- GC with a flame ionisation detector (FID)
- Lighter fuel analysis can be analysed by headspace GC-FID
What are the two purposes of explosives legislation?
- Health and Safety
- Control and safe use of legitimately held explosives 🡪 e.g. 1875 Explosives Act
- Criminal Activity
- Intent to cause harm 🡪 e.g. 1883 Explosive Substances Act
1883 Explosive Substances Act
Offences:
- 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
What does the ‘explosive substance’ term include in the 1883 explosive substances act?
“The expression ‘explosive substance’ shall be deemed to include any materials for making any explosive substance; also any apparatus, machine, implement or materials used, or intended to be used, or adapted for causing, or aiding in causing, any explosion in or with any explosive substance; also any part of any such apparatus, machine or implement”
Where does the burden of proof lie in the 1883 Explosive Substances Act?
- The burden of proof is with the accused
- If you are found to have explosive materials, it is up to you to prove that you don’t intend to use it for illegal purposes (not tending to cause harm)
What was the problem with the 1883 Explosive Substances Act?
It didn’t define what an explosive was
How did they overcome the issue with the 1883 Explosive Substances Act?
They made an amendment that listed the different types of explosives but it’s not all-encompassing as there are lots of other things that could be used as an explosive to cause harm
What case introduced the amendment of what an explosive was for the 1833 Explosives Substances Act?
- R vs Wheatley 1979
- “gun powder, nitroglycerine, dynamite, gun-cotton, 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 producing a practical effect by explosion or a pyrotechnic effect”
1991 Montreal Convention
- More restrictions were introduced relating to the use of plastic explosives
- The use of taggants was introduced
2003 Ammonium Nitrate Regulations
Only farmers could obtain ammonium nitrate in volumes higher than 16%
EU 98/2014 and Control of Explosive Precursors Act 2014
Restrictions on peroxides
Regulated/reported precursors
Controlled % (w/w)
H2O2 = 12%
Nitromethane = 30%
HNO3 = 3%
Na/KClO3 = 40%
KClO4 = 40%
First example of banning membership of an organisation (IRA and INLA)
Counter Terrorist Legislation
Counter-terrorist legislation
- Complimentary to Explosives Act
- First example of banning membership of an organisation (IRA and INLA)
- It was considered an offence to commission, prepare or instigate terrorist activity
- Introduced detention without charge for 48 hours and 5 days with ministerial approval
- This was introduced in the 1970s
2000 Terrorist Act / 2005 Prevention of Terrorism Act
- The potential to make explosives had to be proved it wasn’t for the use of harmful purposes
- Incitement, training and possession of documents were considered new offences
- A broader definition of terrorism was changed to “causing fear in the pursuit of political objectives”
- Proscribed organisations were extended beyond Ireland
- Band 1 Offences were introduced
What are band 1 offences under the 2000 terrorist act / 2005 prevention of terrorism act
Band 1 offences:
- Terrorist murder
- Explosive substances offences
- Preparation for terrorism
- Possession of material for the purpose of terrorism
2006 / 2008 legislation
- New offence 🡪 ‘glorifying’ terrorism/disseminating terrorist publications (Al-Muhajiroun)
- Detention without charge now 28 days and remains the same now (Labour Home Secretary wanted 90)
- Detention time was extended due to cases becoming more complex
- Can continue to question suspects after being charged
- DNA and fingerprints taken from those subject to a ‘control order’
(Often those suspected of terrorism but limited evidence against them)
What do the codes of practise and conduct lay out?
They outline the requirements for being an expert witness
What are the requirements for being an expert witness in relation to terrorism?
- An expert witness only requires “skills beyond those of ordinary people enjoying ordinary pursuits”
- Presents relevant evidence (including opinion evidence.
even allowed to give specialist hearsay evidence!) - If you’re working in an explosive analysis lab and you had a conversation with a supervisor who had an expertise that guided you on how to present or conduct your analysis, you can use this as justification as to why you’ve done something.
What are duties of an expert witness?
To provide evidence which is:
- Independent
- Unbiased
- Impartial
- Objective
- Present their evidence, what they’ve done and why.
- Not to act as an advocate or fact finder
What is the key thing related to explosive legislation and counter-terrorism legislation?
- There are specific codes of practice that we have to adhere to if we’re going to collect and present that evidence in court.
- These include standing operating procedures (SOPs), ISO 17025, etc
