Lecture 6 Flashcards
What is the purpose of an explosive investigation?
- An initial investigation is done to find out what happened
- To determine what we can prove happened within specific parameters
- To present evidence at trial
What are the different types of scientific evidence?
- Classification
- Identification
- Quantification
Classification
- Are these explosives linked?
- If you found some explosive residues can that be linked to another source?
- Can we work out where it came from or where it was made?
- Can we be sure it’s linked to the IED that’s been detonated?
Identification
Is it TNT?
Quantification?
- How much explosive material has been used?
- This is important if someone uses larger amounts which has the potential to cause much more harm.
- This can also be helpful if someone claims it was an accidental detonation because there are legal restrictions on how much material can be stored at once.
What are the 3 S’s in an explosive investigation?
- Selectivity
- Specificity
- Sensitivity
Selectivity
Ability to determine an analyte from a mixture without other components (which vary!) interfering
Specificity
Nothing other than the desired analyte contributes to the result
Confident that nothing else can contribute to the result we are claiming
Sensitivity
Linear slope of the response (calibration curve)
Related to the amount and the limits of detection and quantification
Method, sample prep, volumes used all relate to this
What locations would we want to detect explosive residue from?
- Suspects hands
- Clandestine labs or explosive storage dumps
- Explosion scenes
Explosion scenes
Can also be a failed or accidental explosion scene
Clandestine labs or explosive storage dumps
- Need to take a lot of evidence
- Look around the site for source of reagents used to make the explosives
- The way the explosives are stored and planned to be detonated
The materials and other aspects can be important evidence to build the case
Suspects hands
Take evidence from their hands, clothes, skin and other areas.
What should you check before starting an investigation at an explosion scene?
- You have to make sure the scene is safe before starting an investigation
- Any unexploded devices need to be rendered safe by an explosive ordinance technician
Once checking the scene is safe, what should you do?
- The first thing you should do once it’s safe is to check to see if the explosive contains a viable device.
Then look at the design, does it have the potential to actually be an effective explosive?
What should you consider when starting an explosive investigation?
- Check if it contains a viable device.
- From the design, does it have the potential to be an effective explosive?
- Does it resemble anything encountered before?
- Are they using materials to make illicit explosives?
- Was a condensed phase (solid or liquid) explosive used?
- What was the explosive?
- How was it used?
- How was it initiated?
- Was it intended to cause harm or panic?
- Was it used in the right way and used correctly for the type of explosive it is?
What needs to be considered when investigating an explosive that hasn’t been encountered before?
If it hasn’t been encountered before than additional precautions need to be taken - determine the chastity and volatility of the explosive, the housing and how it tended to be detonated
Why is it easier if an explosive has been encountered before?
If it has been encountered before it makes it easier as you will know its properties better.
What can the state of the explosive tell you?
Particulates and droplets tells you about the materials that might have been used
What should be true for an explosive from a military device?
If it was a military device it would have some form of tag that can identify it
What can be used to identify volatile components?
Mobile GC can be used to identify volatile components
How can you find the point of detonation?
- The point of detonation is usually recognised by a crater
- If the ground is ‘soft’ it is relatively easy to find
What is the problem with a detonation that isn’t in the floor?
If it’s been detonated on something other than the floor a lot of the material gets blown away so determining the specific detonation point can be challenging.
How can you protect the scene from contamination?
All personnel wear overalls, gloves, shoe covers, etc. to protect the scene
Why is an accurate cordon important?
Evidence may be scattered a considerable distance which is dependant on type of explosive, amount of gas generated, etc
What should be collected from an explosive scene?
- All loose soil and debris to be collected from the scene and surroundings
- These should be packaged securely in sealed and properly labelled containers
What may be found embedded in soft objects?
Residues may be found embedded in nearby soft objects (wood, rubber, bodies), this is often true for metal shards.
Where else may residues be found?
- Residues are also found on surfaces of nearby metal objects, e.g. road signs
- Don’t just look at the floor, look around.
What should the entire area be searched for?
Entire area searched for remains of detonating mechanisms and the explosive container
Detonator based evidence
- Blasting cap,
- Electronic timer,
- Mobile phone, etc.
Explosive container pieces
- Pipe section,
- Pipe cap,
- Pipe threads,
- Melted/deformed plastic tubs, etc.
What residue would high and low explosives leave?
- High explosives typically leave very small quantities of residue
- Propellants and low explosives may leave larger quantities
What is a reoccurring problem with improvised explosive devices?
Improvised explosive devices often don’t fully explode or have a detonator malfunction (as in London 21st July 2005 copycat bombing)
How can rapid screening of bulk residues be accomplished?
Rapid screening for bulk residues can be accomplished using a portable instruments like a ‘suitcase GC’ or handheld Raman
What type of explosive leaves the most evidence behind?
propellants and low explosives
What does SEM allow us to look at for explosives?
SEM allows us to look at detail at specific particulates, arrangement and size of fragments
What can we obtain from EDX?
EDX allows us to get elemental identification however it is time consuming so you should make a decision on what to look at and prioritise)
Why is GC used over HPLC?
GC is used more often as it can be used on volatile components
What is ion chromatography used for?
It can detect nitrates and chlorates
Mass Spectrometry
it is very sensitive so it’s good for trace amounts but it isn’t always the best detection method.
Detectors used for explosive analysis
- Mass Spectrometry
- UV Vis
- Flame Ionisation
- Ion Mobility
Spectroscopy used for explosive analysis
- IR / Raman (Quick and Non-destructive)
- X-ray (SEM & EDX)
Separation Methods used for Explosive Analysis
- HPLC
- GC
- Ion Chromatography
- Electrophoresis
What is required for trace explosive analysis?
- Clean rooms
- The background level of explosive material is extremely tightly controlled and well known.
What do clean rooms ensure?
They ensure evidence is uncontaminated and admissible in court
What are the control measures in a clean room?
- Positive pressure
- High-Efficiency Particulate Air (HEPA) Filters
- Air particulate monitoring
- Disposable equipment
Positive pressure
- Contaminants diffuse out of the controlled environment, and won’t allow any contaminants in.
- The pressure is set higher than it is outside.
- This means the contaminants migrate away naturally.
High Efficiency Particulate Air Filters
This is done for the removal of contaminant particulates
Air Particulate Monitoring
Air quality is monitored regularly to keep an eye on background levels and reviewed regularly. If anything goes up a particular level then it is investigated.
Disposable Equipment
Gloves, shoe covers, lab coats, etc. that are double bagged on entry/exit
What is the biggest source of contamination in a clean room?
The biggest source of contamination in a clean room is the analyst themselves as they’re bringing contaminants in from outside.
Examination Area
- Examination area when the evidence is processed and prepared.
- This helps to prevent the spread of different contaminants
How is the integrity maintained in a cleanroom?
- Regular monitoring is used to maintain explosive cleanroom integrity
- Environmental samples taken regularly
What action should be taken if an explosive residue is <5 ng?
No action needs to be taken
What action should be taken if an explosive residue is between 5-10ng?
Confirm the identify of the explosive and clean the area
What action should be taken if an explosive residue is between 10-100 ng?
Clean area and re-test until sample tests negative, all analysis is paused to make sure the levels go back down.
What action should be taken if an explosive residue is >100 ng?
- This is Serious contamination.
- Conduct enquiry to identify the contamination source and the type of contaminant it is.
- Review potentially affected casework and decide how it might have affected it.
- Clean and re-test until negative.
- This doesn’t mean it would be admissible in court but it does need to be investigated
What is the problem with explosive evidence?
- This type of evidence can be difficult to bag
- Packing the evidence correctly along with labelling is very important
What does bulk analysis mean?
- Bulk refers to mg or more
- Quantitative analysis
- Spectroscopy paired with non chemical evidence
What does trace analysis refer to?
- Trace refers to 10 to 100 ng
- Often challenged in court
- Needs to be ‘watertight’ 🡪 clean room techniques
- The higher uncertainties are associated with this type of evidence
What is headspace sampling used for?
Extraction of vapours for detection of volatile explosives and taggants
How are trace explosives processed?
Extraction of vapours for detection of volatile explosives and taggants
What are the two different types of headspace sampling used?
- Static Headspace Sampling
- Dynamic Headspace Sampling
Static Headspace Sampling
- Sample is placed in a sealed vial
- Sample is heated up so the volatiles go into headspace
- Headspace injection is done to extract the vapours and perform a GC analysis
Dynamic Headspace sampling
- Sample is placed in a secure vial
- An interest gas is pushed through
- Inert gas pulls out the volatiles
- Headspace volatiles is drawn into a solid phase trap
- The trap retains the explosive vapours
- Concentrates sample before GC injection
- Useful for trace quantities
Solid Phase Microextraction (SPME)
- Pre-concentration step before injection
- Fused silica fibre coated with stationary phase
- Stationary phase is usually PDMS
- Desorb (by heating) from stationary phase into GC injector
What does the dual function of SPME allow for?
- Trace sample recovery
- Preconcentration of sample
Purpose of the SPME fibre
- Use the SPME fibre so that the volatiles adhere strongly to
- Coated with a similar material used in columns eg PDMS
- This allows for a build up of the sample to increase the quantity we have
How are particulate samples recovered?
- Swabbing
- Vacuuming
- Solvent wash
Swabbing
- Smooth surfaces
- Solvent is a polar mixture 🡪 e.g. water/acetone or water/MeOH
Vacuuming
- Good for fabric + particulates
- Controlled tiny vacuums with filters that can bag evidence efficiently
Solvent wash
- Sonicate the whole sample in a suitable extraction solvent
- Submerge the whole sample
How are samples cleaned/pre-concentrated?
- Solid Phase Extraction
- Used to preconcentrate liquid samples
- It is a small cartridge containing a sorbent material
What are the different forms of Solid Phase Extraction (SPE)
- Normal phase
- Reverse phase
- Ion exchange
- Size exclusion
- You can use a combination of these methods
Normal phase SPE
Adsorbs polar components strongly (A)
Reverse phase SPE
Adsorbs non-polar components strongly (B)
Ion exchange SPE
Used for inorganic type components
Size Exclusion SPE
- Absorbs lower molecular weight strongly.
- If you have a mixture of large and small this method might be preferable
Conditioning of Reverse phase SPE
- Clean the sorbent using ethyl acetate. This prepares the sample
- Condition the sorbent using ethanol and water mixture (polar mix)
- Apply sample (ethanol and water extract)
- Analyse for inorganic species. The non-polar components stick to the non-polar sorbent in the cartidge
- Wash sorbent with ethanol and water mix
- Wash sorbent with MTBE and Pentane mix
- This wash is done to wash out the non-polar components
- Ethyl acetate is used to elute explosives
- Analyse for organic high explosives
In reverse phase SPE what does ethyl acetate do?
It prepares the sample
What happens to the non polar sorbents in SPE?
Non polar components stick to the non polar sorbent in the cartridge
How do we analyse explosives?
A separatory system combined with an explosive specific detection system
Whats the problem with using standard analytical techniques to analyse explosives?
- Standard analytical techniques (GC/MS, LC/MS) don’t always provide sufficient evidence
- Non-explosive compounds may have very similar molecular weights and retention times
What are the detectors used for the analysis of explosives?
- Chemiluminscence
- Thermal Energy Analyser
Chemiluminscence Detector
C-NO2, N-NO2, O-NO2 groups
Thermal Energy Analyser
- Controlled pyrolysis to form NO
- Pyrolysis is the thermal decomposition in the absence of air
