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Materials Identification > organic GSR > Flashcards

organic GSR Flashcards

1
Q

what is organic GSR

A

GSR derived from the combustion of propellant materials

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2
Q

give 4 examples of GSR

A

Cellulose nitrate

Nitroglyercol

Nitroguanidine

Other propellants such as additives

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3
Q

which is more significant, organic GSR or inorganic GSR?

A

inorganic

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4
Q

cellulose nitrate does not contain what

A

the necessary oxygen to combust fully

Negative oxygen balance

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5
Q

some unburned material leaves…..

A

the barrel without further oxidation often due under-ignition

Combustion completes upon combination with the atmosphere producing characteristic flash

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6
Q

residues of partial combustion are formed including what

A

Nitrates and Nitrites along with unchanged additive components

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7
Q

give 3 examples of incomplete combustion products

A

Unchanged additive components such as Ethyl Centralite

Nitrates – R-NO3 – In many cases Nitrocellulose itself!

Nitrites – R-NO2

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8
Q

give 2 examples of presumptive tests for nitrates

A

dermal nitrate test

modified Griess test

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9
Q

dermal nitrate test for nitrates

A

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

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10
Q

what is a positive reaction for nitrates in the dermal nitrate test

A

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

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11
Q

what are 3 false positives for the dermal nitrate test

A

ferric iron
nitrate
dichromate

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12
Q

Griess test (no longer used)

A

Hands or suspect areas swabbed using dilute Nitric acid

Swab treated with Griess reagent – diazotisation

  • Sulfanilamide (2%)
  • Naphthylethylenediamine dihydrochloride (0.2%)
  • Phosphoric acid (5%)
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13
Q

positive reaction for nitrates in Griess test (no longer used)

A

Colour change to pink indicated presence of nitrites

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14
Q

problems with Griess test (no longer used)

A

Numerous false negatives

False positives

Poor reputation (Birmingham six)

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15
Q

modified Griess test for nitrates

A

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

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16
Q

positive reaction for nitrates in Griess test

A

Colour change to orange indicates presence of nitrites

17
Q

why should the Griess test not be used as a confirmatory test

A

Numerous false negatives

False positives

18
Q

give 5 environmental applications of nitrates

A
  • 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…

19
Q

what are nitrates based upon

A

NO3-

20
Q

what are nitrites based upon

A

NO2-

21
Q

give 5 applications of nitrites

A

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

22
Q

lab analysis of GSR

A

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.
23
Q

see powerpoint for

A

compound and purpose table

24
Q

gas chromatography - lab analysis

A

Generally an excellent technique for the separation and detection of individual explosive or propellant components

Specific detection regimes may have excellent sensitivity (MS)

Rapid

25
Q

high performance LC - lab analysis

A

A serious competitor to GC

Sensitivity detection specific

26
Q

MECE - Micellelar electrokinetic capillary electrophoresis

A

GSR becomes encapsulated in micelles

These undergo electrophoresis

Very rapid

27
Q

what does MECE stand for

A

Micellelar electrokinetic capillary electrophoresis

28
Q

TEA – Thermal energy analysis

A

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

29
Q

what does TEA stand for?

A

Thermal energy analysis

30
Q

what does ECD stand fir

A

electrochemical detection

31
Q

ECD – Electrochemical detection

A

Various options

PDME – Pendulum drop mercury electrode has been successful in some providers
Non-Specific

Sensitivity for NC ~100pg

32
Q

MS – Mass spectrometry

A

In many ways the method of choice

Definitive results

Sensitivity excellent ~2.5pg possible

33
Q

environmental sources of o-GSR

A

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

Materials Identification (17 decks)

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