organic GSR

Question 1

what is organic GSR

Answer 1

GSR derived from the combustion of propellant materials

Question 2

give 4 examples of GSR

Answer 2

Cellulose nitrate

Nitroglyercol

Nitroguanidine

Other propellants such as additives

Question 3

which is more significant, organic GSR or inorganic GSR?

Answer 3

inorganic

Question 4

cellulose nitrate does not contain what

Answer 4

the necessary oxygen to combust fully

Negative oxygen balance

Question 5

some unburned material leaves…..

Answer 5

the barrel without further oxidation often due under-ignition

Combustion completes upon combination with the atmosphere producing characteristic flash

Question 6

residues of partial combustion are formed including what

Answer 6

Nitrates and Nitrites along with unchanged additive components

Question 7

give 3 examples of incomplete combustion products

Answer 7

Unchanged additive components such as Ethyl Centralite

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

Nitrites – R-NO2

Question 8

give 2 examples of presumptive tests for nitrates

Answer 8

dermal nitrate test

modified Griess test

Question 9

dermal nitrate test for nitrates

Answer 9

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

Question 10

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

Answer 10

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

Question 11

what are 3 false positives for the dermal nitrate test

Answer 11

ferric iron
nitrate
dichromate

Question 12

Griess test (no longer used)

Answer 12

Hands or suspect areas swabbed using dilute Nitric acid

Swab treated with Griess reagent – diazotisation

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

Question 13

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

Answer 13

Colour change to pink indicated presence of nitrites

Question 14

problems with Griess test (no longer used)

Answer 14

Numerous false negatives

False positives

Poor reputation (Birmingham six)

Question 15

modified Griess test for nitrates

Answer 15

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

Question 16

positive reaction for nitrates in Griess test

Answer 16

Colour change to orange indicates presence of nitrites

Question 17

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

Answer 17

Numerous false negatives

False positives

Question 18

give 5 environmental applications of nitrates

Answer 18

• 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…

Question 19

what are nitrates based upon

Answer 19

NO3-

Question 20

what are nitrites based upon

Answer 20

NO2-

Question 21

give 5 applications of nitrites

Answer 21

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

Question 22

lab analysis of GSR

Answer 22

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.

Question 23

see powerpoint for

Answer 23

compound and purpose table

Question 24

gas chromatography - lab analysis

Answer 24

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

Specific detection regimes may have excellent sensitivity (MS)

Rapid

Question 25

high performance LC - lab analysis

Answer 25

A serious competitor to GC Sensitivity detection specific

Question 26

MECE - Micellelar electrokinetic capillary electrophoresis

Answer 26

GSR becomes encapsulated in micelles These undergo electrophoresis Very rapid

Question 27

what does MECE stand for

Answer 27

Micellelar electrokinetic capillary electrophoresis

Question 28

TEA – Thermal energy analysis

Answer 28

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

Question 29

what does TEA stand for?

Answer 29

Thermal energy analysis

Question 30

what does ECD stand fir

Answer 30

electrochemical detection

Question 31

ECD – Electrochemical detection

Answer 31

Various options PDME – Pendulum drop mercury electrode has been successful in some providers Non-Specific Sensitivity for NC ~100pg

Question 32

MS – Mass spectrometry

Answer 32

In many ways the method of choice Definitive results Sensitivity excellent ~2.5pg possible

Question 33

environmental sources of o-GSR

Answer 33

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