organic GSR Flashcards
organic GSR
o-GSR
GSR derived from
the combustion of propellant materials: • Cellulose Nitrate • Nitroglyercol • Nitroguanidine • Most importantly other propellant components such as additives
Organic GSR
- Arguably of significantly less evidential value than p-GSR (inorganic)
- More common in the environment
- Requires a very different analytical approach
- SEM-EDX inappropriate
propellants
- Cellulose nitrate alone does not contain the necessary oxygen to combust fully
- Negative oxygen balance
- Ideal combustion of pure cellulose hexanitrate would produce…
- C12H14(NO3)6O7 = 9CO2 + 3CO + 7H2O + 3N2
in practice complete combustion does not occur
- Some unburned material leaves the barrel without further oxidation often due under-ignition
- Combustion completes upon combination with the atmosphere producing characteristic flash
residues of partial combustion
• Nitrates and Nitrites along with unchanged additive component
Incomplete combustion products
- Most commonly
- Unchanged additive components such as Ethyl Centralite
- Nitrates – R-NO3 – In many cases Nitrocellulose itself!
- Nitrites – R-NO2
- These may be of evidential value but this is limited by their presence in the environmental in numerous guises
- Various sources for both classes of compounds
Presumptive tests
Dermal nitrate test – Nitrates
- Used for many years for the detection of explosives
- Hands or suspect areas covered in a layer of molten paraffin wax
- This involves a suspect dipping hands in a bucket of heated wax (H&S!)
- Allowed to cool and solidify
- Wax ‘gloves’ removed
Dermal nitrate test – Nitrates
cast treated
- 3% diphenylamine in 95% sulphuric acid
- This is pipetted on drop by drop and observed
- A positive reaction gives a blue colouration in areas where nitrates are present
- Normally tiny blue specks
Dermal nitrate test – Nitrates
reaction mechanism
- Quite a complex reaction in real terms
- Sulphuric acid reacts with nitrates forming nitric acid
- H2SO4 + 2NO3- = SO42- + 2HNO3
- Nitric acid formed reacts with diphenylamine to form a blue coloured compound diphenylbenzidine blue
Dermal nitrate test – Nitrates
considered unreliable
- Numerous false negatives
- False positives
- Ferric ion
- Nitrite
- Dichromate
Presumptive tests Griess Test (No longer used) – Nitrites
- Used for many years for the detection of explosives
- Hands or suspect areas swabbed using dilute Nitric acid
- Swab treated with Griess reagent – diazotisation
- Sulfanilamide (2%)
- Naphthylethylenediamine dihydrochloride (0.2%)
- Phosphoric acid (5%)
- Colour change to pink indicates presence of nitrites
Griess Test (No longer used) – Nitrites
considered unreliable
- Numerous false negatives
- False positives
- Poor reputation (Birmingham six)
Common test for nitrites
Modified Griess test – Nitrites
- Used as a presumptive test for location of potential GSR
- Developed to replace the suspected carcinogenic used in the Griess test
- Improvement in colour reaction compared to Griess
• Sulphanilic acid
• Alpha napthol
• Combined and absorbed onto medium
• Acetic acid (15%) steam activates the reaction - Colour change to orange indicates presence of nitrites
Modified Griess test – Nitrites
Not to be used a confirmatory test
- Numerous false negatives
- False positives
nitrates
• Nitrates are based upon the NO3- ion
Nitrates are based upon the NO3- ion
Nitrates have numerous environmental applications including:
- Fertilisers – Ammonium Nitrate (NH4NO3) itself an explosive!
- Oxidising agents – Barium and Potassium nitrates (Fireworks)
- Preservatives – Sodium Nitrate (E251)
- Nitro Glycerol (GTN) – Treatment for angina
- Amyl Nitrate – Poppers…
- Cellulose nitrate itself!
Be aware of all of the environmental sources of nitrites as these could have significant bearing on a GSR case
• Ascertaining current employment, use of medicines and ‘hobbies’ of the suspect is a wise precaution
nitrites
• Nitrites are based upon the NO2- ion
Nitrites are based upon the NO2- ion
Nitrites have fewer obvious applications:
- Preserving agents – Sodium Nitrite (E250) and Potassium Nitrite (E249)
- Especially cured products such as bacon salami etc.
- Dyeing industry – Nitrites may be used in the manufacture of azo-dyes
- Photography – Developers
- Rodenticide – Ammonium Nitrite
- Industry – Various applications
Be aware of all of the possible environmental sources of nitrites
• Be aware of employment which may bring a suspect into contact with these compounds
Laboratory analysis of o-GSR
• A variety of detection protocols
• Gas Chromatography
- Generally an excellent technique for the separation and detection of individual explosive or propellant components
- Specific detection regimes may have excellent sensitivity (MS)
- Rapid
Laboratory analysis of o-GSR
• A variety of detection protocols
High performance LC
- A serious competitor to GC
* Sensitivity detection specific
Laboratory analysis of o-GSR
• A variety of detection protocols
MECE
Micellelar electrokinetic capillary electrophoresis
• GSR becomes encapsulated in micelles
• These undergo electrophoresis
• Very rapid
detection TEA
Thermal energy analysis
• For GSR, the eluted compound enters a heated chamber nitrates forming nitrogen dioxide and the NO radical under the same conditions
• The NO is swept into an ozone chamber where upon it converts to excited nitrogen dioxide
• When this drops to ground state it emits light in the 600-1000nm region which can be detected and quantified
• Selective for compounds which can form nitrate or nitrite
• Low ng sensitivity
detection ECD
Electrochemical detection • Various options • PDME – Pendulum drop mercury electrode has been successful in some providers • Non-Specific • Sensitivity for NC ~100pg
