organic GSR Flashcards
what is organic GSR
GSR derived from the combustion of propellant materials
give 4 examples of GSR
Cellulose nitrate
Nitroglyercol
Nitroguanidine
Other propellants such as additives
which is more significant, organic GSR or inorganic GSR?
inorganic
cellulose nitrate does not contain what
the necessary oxygen to combust fully
Negative oxygen balance
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 are formed including what
Nitrates and Nitrites along with unchanged additive components
give 3 examples of incomplete combustion products
Unchanged additive components such as Ethyl Centralite
Nitrates – R-NO3 – In many cases Nitrocellulose itself!
Nitrites – R-NO2
give 2 examples of presumptive tests for nitrates
dermal nitrate test
modified Griess test
dermal nitrate test for nitrates
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
Casts treated
3% diphenylamine in 95% sulphuric acid
This is pipetted on drop by drop and observed
what is a positive reaction for nitrates in the dermal nitrate test
A positive reaction gives a blue colouration in areas where nitrates are present
Normally tiny blue specks
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
what are 3 false positives for the dermal nitrate test
ferric iron
nitrate
dichromate
Griess test (no longer used)
Hands or suspect areas swabbed using dilute Nitric acid
Swab treated with Griess reagent – diazotisation
- Sulfanilamide (2%)
- Naphthylethylenediamine dihydrochloride (0.2%)
- Phosphoric acid (5%)
positive reaction for nitrates in Griess test (no longer used)
Colour change to pink indicated presence of nitrites
problems with Griess test (no longer used)
Numerous false negatives
False positives
Poor reputation (Birmingham six)
modified Griess test for nitrates
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
positive reaction for nitrates in Griess test
Colour change to orange indicates presence of nitrites
why should the Griess test not be used as a confirmatory test
Numerous false negatives
False positives
give 5 environmental applications of nitrates
- 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…
what are nitrates based upon
NO3-
what are nitrites based upon
NO2-
give 5 applications of nitrites
Preserving agents – Sodium Nitrite (E250) and Potassium Nitrite (E249)
Dyeing industry – Nitrites may be used in the manufacture of azo-dyes
Photography – Developers
Rodenticide – Ammonium Nitrite
Industry – Various applications
lab analysis of GSR
Much of the analysis of o-GSR can be based on analysis for specific compounds not general classes
- Nitrocellulose
- Nitroglycerine
- Additives such as Ethylcentralite etc.
see powerpoint for
compound and purpose table
gas chromatography - lab analysis
Generally an excellent technique for the separation and detection of individual explosive or propellant components
Specific detection regimes may have excellent sensitivity (MS)
Rapid
high performance LC - lab analysis
A serious competitor to GC
Sensitivity detection specific
MECE - Micellelar electrokinetic capillary electrophoresis
GSR becomes encapsulated in micelles
These undergo electrophoresis
Very rapid
what does MECE stand for
Micellelar electrokinetic capillary electrophoresis
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
what does TEA stand for?
Thermal energy analysis
what does ECD stand fir
electrochemical detection
ECD – Electrochemical detection
Various options
PDME – Pendulum drop mercury electrode has been successful in some providers
Non-Specific
Sensitivity for NC ~100pg
MS – Mass spectrometry
In many ways the method of choice
Definitive results
Sensitivity excellent ~2.5pg possible
environmental sources of o-GSR
Sources of specific organic residues include
- Cellulose Nitrate – Paints, lacquers, molecular biology
and even ping pong balls
- Nitro glycerol – Treatment for angina
- Nitroguinidine – May be present in insecticides or Jetex pellets
- Ethylcentralite – Plasticisers for celluloid materials (Uncommon)
- 2,4 DNT – Polymer industry (Foam manufacture)
- Triacetin – Various sources inclusing food additive (Common)
- Diphenylamine – Antioxidant and anti-fungal
