What are the three types of scientfic evidence when doing an explosive investigation?
- Classification - are the explosives linked
- Identification
- Quantification - how much
What are the three S’s in an explosive investigation?
- Selectivity - ability to determine an analyte from a mixture without other components interfering
- Specificity - Nothing other than desired analyte contributes to the results
- Sensitivity - limit of detection and quantification (specific to instruments and sample prep)
What locations would we want to detect explosive residue from?
- Suspects hands and clothes and other areas of skin where GSR could be
- Clandestine labs or explosive storage dumps (explosion sites might not have a lot of evidence but where it was made or stored could)
- Explosion scenes
What are some post explosive scene considerations?
- Forensic scientists shouldnt go near it until it is deemed safe
- Then need to see if it has the potential to be an effective explosive
- If it has been encountered before you can know the explosive power and what evidence you want to look for first
- If it hasnt, additional measurments need to be taken
Where are some points of collection of explosive residues
- Point of detonation is usually identified by a crater, unless the detonation didnt happen on the ground
- All loose soil and debris to be collected
- Residues may be embedded in nearby soft objects (wood, rubber, bodies) or near metal surfaces (road signs)
What are examples of different remains that could be found?
- Detonator based evidence = blasting cap, electronic timer, mobile phone
- Explosive contrainer pieces = pipe section, pipe cap, pipe threads, melted/deformed plastic tubs
What are some analytical equipment used to anaylse explosive residues?
Spectroscopy:
* IR/Raman - non destructive
* X-Ray (SEM, EDX) - look at morphorlogical characteristics
Separation:
* HPLC/GC - volatile components
* Ion chromatography - nitrates an chlorate detection
* Electrophoresis
Detectors:
* MS - not always the ebst but is sensitive
* UV/vis
* Flame ionisation
* Ion mobility
Clean room techniques
- Required for trace explosive analysis
- Ensure evidence is uncontaminated and admissible in court
- Pressure of lab is higher than outside so contaminants will migrate out of the clean room
What are the 4 control measures in clean rooms?
- Positive pressure: contaminents diffuse out of the controlled environment
- High efficiency particulate air (HEPA) filters: removal of contraminant particulates
- Air particulate monitoring
- Disposable equipment: gloves, shoe covers, lab coats all double bagged on entry/exit
What are the different actions taken with different amounts of explosive residues in the environmentof a clean room?
All measurments in ng
* <5 - none
* 5-10 - confirm identity of explosive and clean area
* 10-100 - clean area and re-test until sample tests negative, stop all analysis until levels go down
* >100 - conduct enquiry to identify contamination source, review potentially affected casework, clean and re-test until negative
How are trace explosives processed?
- Static headspace sampling - sample placed into a sealed container, heated, headspace injection into GC
- Dynamic headspace sampling - headspace drawn into a solid phase trap, retains explosive vapours, concentrates sample before GC injection, good for trace
- Solid phase microextraction (SPME) - pre-concentration step before injection, fused silica fibre coated with stationary phase, desorb by heating from stationary phase into GC injector
How are particulate samples recovered?
- Swabbing - smooth surfaces, solvent is a polar mixture (water/acetone or water/MeOH)
- Vacuuming - good for fabric
- Solvent wash - sonicate the whole sample in a suitable extraction solvent, submerge a whole sample
How are samples ‘cleaned’/pre-concentrated?
Solid phase extraction - small cartridge containing a sorbent material (can do all these together):
* Normal phase - adsorbs polar components strongly
* Reverse phase - adsorbs non-polar components strongly
* Ion exchange - inorganic components
* Size exclusion - adsorbs lower molecular weight strongly, mixture of large and small
How do we analyse the explosives?
- A separatory system combined with detection system
- Standard analytical techniques arent always great (non-explosive components may have similar molecular weights and retention times)
- Explosive-specific detection systems - chemiliminescence (detection of X-NO2 groups), thermal energy analyser (controlled pyrolysis to form NO)
