The analysis of unfired propellant particles by gas chromatography mass spectrometry a forensic approach

THE ANALYSIS
OF
UNFIRED PROPELLANT PARTICLES
BY
GAS CHROMATOGRAPHY –
MASS SPECTROMETRY:

A
FORENSIC APPROACH
A thesis presented to the

Queensland University of Technology

in fulfilment of the requirements for the degree of

Masters of Applied Science (Research)

by

Shiona Croft
Bachelor of Applied Science

Under the Supervision of:

Dr John Bartley
School of Physical and Chemical Sciences
Queensland University of Technology
April 2008


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In Australia, the 0.22 calibre ammunition is the most encountered ammunition type
found at a crime scene [1]. Previous analysis of gun shot residue (GSR) and unfired
propellant has involved studying the inorganic constituents by Scanning Electron
Microscopy or similar technique. However, due to the heavy metal build up that
comes with some ammunition types, manufacturing companies are now making
propellant that is safer to use. Therefore, it has become appropriate to study and
analyse unfired propellant by other means. One such technique is unfired propellant
analysis by gas chromatography – mass spectrometry (GC-MS). This technique
focuses on the organic constituent make up of the propellant paying particular
attention to diphenylamine, ethyl centralite and dibutyl phthalate. It was proposed
that different batches of ammunition could be discriminated or matched to each other
by using this technique. However, since the main constituents of unfired propellant
are highly reactive, it was not possible to accomplish batch determination of
ammunition. However, by improving extraction techniques and by removing oxygen
(a catalyst for the degradation of diphenylamine) a superior method was established
to help in the analysis of unfired propellant. Furthermore, it was shown that whilst
differentiating batches of the same ammunition was not possible, the improved
methods have helped identify different types of the same brand of ammunition. With
the aid of future studies to fully explore this avenue, the analysis of unfired
propellant could one day become an integral part of forensic science.

The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
Shiona Croft

ii


67$7(0(17 2) 25,*,1$/ $87+256+,3
The work contained in this thesis has not been previously submitted to meet
requirements for an award at this or any other higher education institution. To the

best of my knowledge and belief, the thesis contains no material previously
published or written by another person except where due reference is made.

Shiona Croft

Date

The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
Shiona Croft

iii


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I wish to thank all those people who over the past years have seen me through my
best and my worst….

Firstly, to my supervisor Dr John Bartley (QUT) for your advise, patience and
support throughout my research. Your expert knowledge and direction was greatly
appreciated. In particular, your considerable experience with mass spectrometry and
research methodologies. Also, for your endless endurance, patience and guidance
with regards to the thesis write up. For all your help, I thank you.

To the Queensland Police Service (Mr Gary Asmussen and the members of the
Analytical Services Unit) for allowing me to take up this research but for also giving
me the freedom to explore this project in the direction I thought most appropriate.
Thank you.

To my colleague and friend Dr Helen Panayiotou, thank you for your words of
wisdom. Your encouragement and valuable direction when I felt lost was appreciated

greatly.

To my mum and dad who has been supportive from day one. Your support,
enthusiasm and confidence in my abilities allowed me to have courage in my work.
Thank you for never allowing me to give up – although I am too stubborn to do so!

To my dear Chris, who everyday told me how proud of me he was. Thank you for
putting up with the late nights and the stress. For your love, friendship and strength –
I honestly could not have done this without you. You mean everything to me.

To my brother Kevin, who I know is very proud of me. Thanks for your support
Kev!

The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
Shiona Croft

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To my Ouma and Grandad, Connie and Gerald Campbell, I wish you could be here
but you are always in my thoughts. Thank you for your support and interest in my
thesis. It means so much to me that even though you are far away your love and
encouragement is not forgotten. I miss you.

To my very much loved group of friends; Scott, Niki, Amy, Mick, Nikki and
everyone else who has been there for me. Some of you have been around for more
than a decade and your love, encouragement and support is never forgotten. You all
mean the world to me and thank you for giving me the strength to go on.

Finally, to all the post graduate students whom I may not have seen as much as I

would have liked (since being off campus) but to my friend Dr Sarah Ede in
particular, who constantly inspired me and who I always knew would do great things.
Thank you.

The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
Shiona Croft

v


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67$7(0(17 2) 25,*,1$/ $87+256+,3 ................................III
$&.12:/('*(0(176 .................................................................... IV
7$%/( 2) &217(176 ......................................................................... VI
/,67 2) ),*85(67$%/(6 ............................................................ VIII
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,1752'8&7,21............................................................................ 1

1.1

BACKGROUND .......................................................................................... 1

1.2

THE 0.22 CALIBRE AMMUNITION .............................................................. 1

1.2.1

The Cartridge ................................................................................... 2

1.2.2

The Projectile.................................................................................... 2

1.2.3

The Propellant .................................................................................. 3

1.2.4

The Primer........................................................................................ 3

1.3

PREVIOUS WORK RELATED TO ORGANIC GUN SHOT RESIDUE OR UNFIRED

PROPELLANT ANALYSIS ........................................................................................ 4



(;3(5,0(17$/ ......................................................................... 18

2.1

MATERIALS ............................................................................................ 18

2.2

INSTRUMENTATION ................................................................................ 18

2.3

STANDARD PREPARATION ....................................................................... 19

2.4

ETHYL ACETATE ALONE PROCEDURE ..................................................... 19

2.5

ETHYL ACETATE/DICHLOROMETHANE PROCEDURE ............................... 19

2.6

CONSISTENCY OF PROPELLANT COMPOSITION EXPERIMENT ................. 20

2.7

EXCLUSION OF OXYGEN EXPERIMENT .................................................... 20

2.8

TYPE DETERMINATION OF WINCHESTER AMMUNITION ......................... 20


3.1

5(68/76 $1' ',6&866,21 .................................................. 22
MASS SPECTRA OF UNFIRED PROPELLANT COMPONENTS ....................... 22

The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
Shiona Croft

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3.1.1

Diphenylamine (C12H11N) ............................................................... 22

3.1.2

Ethyl centralite (C17H20N2O) ........................................................... 24

3.1.3

Dibutyl phthalate (C16H22O4) .......................................................... 26

3.2

CONTROLLED STANDARDS ..................................................................... 28

3.2.1

Diphenylamine, ethyl centralite and dibutyl phthalate variation...... 29

3.3

THE ANALYSIS OF PROPELLANT USING ETHYL ACETATE ALONE ........... 30

3.4

REMOVAL OF THE NITROCELLULOSE COMPONENT OF PROPELLANT USING

ETHYL ACETATE AND DICHLOROMETHANE ........................................................ 44

3.5

CONSISTENCY OF PROPELLANT COMPOSITION FROM A SINGLE

BOX/BATCH OF AMMUNITION ............................................................................. 53

3.6

THE EFFECTS OF EXCLUDING OXYGEN ................................................... 58

3.7

TYPE DETERMINATION OF WINCHESTER AMMUNITION ......................... 65

3.7.1

Winchester Laser LR HP 2DRM41.................................................. 65

3.7.2

Winchester Expert 23DLH02........................................................... 66

3.7.3

Winchester Winner IDKE52 ............................................................ 66

3.7.4

Winchester Subsonic LR Rim fire AED1FH31 ................................. 67

3.7.5

Winchester Superspeed LR HV solid SDSB51.................................. 68

3.7.6

Winchester Superspeed LR HV hollow point 2DRL62...................... 69



&21&/86,216 $1' )8785( :25. ................................. 72

4.1

CONCLUSIONS ........................................................................................ 72

4.2

FUTURE WORK....................................................................................... 73
$33(1',; ............................................................................................... 74

Ethyl Centralite standard ............................................................................... 74
Dibutyl phthalate standard ............................................................................. 75
Diphenylamine standard................................................................................. 76
Winchester Laser Long Rifle Hollow point 2DRM41 ...................................... 77
Winchester Expert 23DLH02 .......................................................................... 78
Winchester Winner IDKE52 ........................................................................... 79
Winchester Subsonic Long rifle Rim fire AED1FH31...................................... 80
Winchester Superspeed Long Rifle High velocity solid 2DSB51...................... 80
Winchester Superspeed long rifle high velocity hollow point 2DRL62............. 81
5()(5(1&(6 ......................................................................................... 82
The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
Shiona Croft

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Figure 1.1: Dissected view of the case [8] ................................................................ 2
Table 1.1: Elution order for constituents using HPLC-MS[29] ................................. 6
Figure 1.2 Degradation of DPA [10,11].................................................................... 7
Table 1.2: Results from Northrop[46,47] ................................................................ 15
Table 3.1: Selected target compounds (from NIST library)..................................... 22
Figure 3.1 Mass spectrum of diphenylamine........................................................... 24
Figure 3.2 Chemical structure of diphenylamine and m/z = 77 fragment ion (C6H5)
.......................................................................................................... 24
Figure 3.3: Ethyl Centralite .................................................................................... 25
Figure 3.4: Mass spectrum of ethyl centralite ......................................................... 25
Figure 3.5: Fragmentation ions of ethyl centralite................................................... 25
Figure 3.6: Fragment A = m/z 120 and Fragment B = m/z 148 ............................... 26
Figure 3.7: General structure of phthalate esters where R, R’ = CnH2n+1; n=415[50] ............................................................................................... 26

Figure 3.8: Characteristic fragmentation ions of butyl phthalate esters [51] ............ 27
Figure 3.9: Mass spectrum and chemical structure of dibutyl phthalate................... 28
Table 3.2 DPA, EC and DBPH standard variation .................................................. 29
Table 3.3 Variation in peak area of DPA between three random propellant samples
and variation observed between the three samples ............................. 31
Figure 3.10: Diphenylamine degradation over time ................................................ 31
Figure 3.11: Sample 1 - diphenylamine degradation ............................................... 32
Figure 3.12: Sample 2 - diphenylamine degradation ............................................... 33
Figure 3.13: Sample 3 - diphenylamine degradation ............................................... 33
Figure 3.14: 2-nitro-diphenylamine amounts detected (three random samples) –
Extrapolated to time zero to give appreciation of initial amounts of 2nitro-DPA in each sample.................................................................. 34
Figure 3.15: Mechanisms of N-Nitroso-DPA in the presence of NO2 and O2 [16] ... 36
Figure 3.16: Lussier and Gagnon [14]: Concentration of DPA and its derivatives as a
function of added nitrogen dioxide .................................................... 37

The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
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Figure 3.17: Effect of storage on diphenylamine concentration (sample one and two)
.......................................................................................................... 38
Figure 3.18: Sample 1 - Effect of storage on diphenylamine (triplicate).................. 39
Figure 3.19: Sample 1 - The effect of storage on 2- nitro-diphenylamine (analysed
three times) ....................................................................................... 40
Figure 3.20: Sample one and two analysed each three times (average): comparison
between stored samples and samples left in solution for one week..... 41
Figure 3.21: The effect of leaving propellant in solution over one week (2-nitro-DPA
average – each sample analysed three times) ..................................... 42

Figure 3.22: Diphenylamine response (EtAc/Ch2Cl2 procedure) ............................. 45
Figure 3.23: Comparison between EtAc alone and EtAc/CH2Cl2 on DPA (average)
.......................................................................................................... 46
Figure 3.24: Comparison of EtAc alone and EtAc/CH2Cl2 procedures - 2-nitro-dpa
(average: each sample analysed three times)...................................... 47
Figure 3.25: 2-nitro-dpa levels - sample 1: comparison between EtAc alone and
EtAc/CH2Cl2 procedures ................................................................... 48
Figure 3.26: Comparison between EtAc alone and EtAc/CH2Cl2 procedures (ethyl
centralite average) ............................................................................. 50
Figure 3.27: Dibutyl phthalate – comparison between EtAc alone and EtAc/CH2Cl2
procedures......................................................................................... 51
Table 3.4: Relationship between sample size and population size ........................... 53
Table 3.5: Masses from ten random samples from one box of ammunition ............. 53
Figure 3.28: Levels of diphenylamine of ten (10) random samples of propellant from
the one box of ammunition ................................................................ 55
Figure 3.29: Levels of dibutyl phthalate detected of ten (10) random samples of
propellant from the one box of ammunition ....................................... 55
Table 3.6: Ratios (peak area) of main constituents from one box of ammunition .... 56
Figure 3.30 Inert gas procedure consequences on the main constituents of unfired
propellant particles ............................................................................ 58
Figure 3.31: Inert gas procedure (dibutyl phthalate)................................................ 60
Figure 3.32: The effects of leaving propellant in solution under an inert atmosphere
.......................................................................................................... 61

The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
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Figures 3.33: Re-analysis of samples A-D 24 hours later (individually separated for
visual clarity) .................................................................................... 63
Figure 3.34: Winchester Laser LR HP 2DRM41 .................................................... 65
Figure 3.35: Winchester Expert 23DLH02 ............................................................. 66
Figure 3.36: Winchester Winner IDKE52............................................................... 67
Figure 3.37: Winchester Subsonic LR Rim fire AED1FH31................................... 68
Figure 3.38: Winchester Superspeed LR HV solid 2DSB51 ................................... 69
Figure 3.39: Winchester Superspeed LR HV hollow point 2DRL62 ....................... 70
Table 3.7: Type determination of Winchester ammunition...................................... 71

The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
Shiona Croft

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CH2Cl2:

Dichloromethane

DBPH:

Dibutyl phthalate

DEPH:

Diethyl phthalate

DNT:

2,4-dinitrotoluene

DPA:

Diphenylamine

EC:

Ethyl centralite

EtAc:

Ethyl Acetate

GC-MS:

Gas chromatography – mass spectrometry

GSR:

Gun shot residue

HP:

Hollow Point

HPLC:

High performance liquid chromatography

HV:

High Velocity

LC:

Liquid chromatography

LR:

Long Rifle

MC:

Methyl centralite

NC:

Nitrocellulose

NG:

Nitro-glycerine

N-nitroso-DPA:

N-nitroso-diphenylamine

OGSR:

Organic gun shot residue

SEM:

Scanning electron microscopy

THC:

Tetrahydrocannabinol

THC acid:

Tetrahydrocannabinol acid

TLC:

Thin layer chromatography

TNT:

Trinitrotoluene

2-nitro-DPA:

2-nitro diphenylamine

4-nitro-DPA:

4-nitro diphenylamine

The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
Shiona Croft

xi




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Gun shot residue analysis has evolved into a significant, integral part of forensic
science today. Increased research into methodology, detection and subsequent
examination of the gunshot residue has allowed this type of evidence to be used more
effectively by analysts for the purpose of solving crime.

One area of research that has been explored is investigating the organic constituents
of unfired propellant to identify their key role in ammunition make up and functions.
It is widely known that the inorganic components of gunshot residue are readily
analysed by the scanning electron microscope to identify lead, barium and antimony
and other key ingredients[2-5]. However, the potential health risks associated with
heavy metal build up, have led to heavy metal free ammunition being introduced [6].
In this situation, organic analysis of the residue or propellant is required and
subsequently, analysts have demonstrated that this is possible. There are some
discrepancies though with which constituents are unique to smokeless powders,
which will aid in the identification of the ammunition.



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In Australia, the use of 0.22 calibre ammunition is wide spread[1] and so,
investigative forces are mostly concerned with this type of ammunition. To fully
appreciate the diversity of the 0.22 calibre projectile some background information
will be given about the physical make up of ammunition itself, including: the
cartridge and cartridge case, projectile, propellant; and primer and their roles in the
organic make-up of the ammunition[1,7].
The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
Shiona Croft

1


1.2.1

The Cartridge

The calibre of the ammunition refers to the diameter of the bore inside the firearm. A
typical cartridge will contain the case, primer, propellant and projectile. The
ammunition can either be rim fire or centre fire. In rim fire ammunition, the priming
materials are concentrated around the outer edge of the base of the cartridge making
the rim the most susceptible to detonation. Conversely, centre fire concentrates the
priming material into the centre of the base of the cartridge leading to this centre
being the most susceptible to ignition.

This figure is not available online.

Please consult the hardcopy thesis
available from the QUT Library

Figure 1.1: Dissected view of the case [8]

1.2.2

The Projectile

Lands and grooves are often marked onto fired projectiles as they spiral out of the
muzzle of the firearm. These physical striations can help in the physical
characterisation of the projectile through the use of a comparison microscope. The
shape, cannelures, dimensions of the hollow point and coating can all be
discriminating identifiers of the projectile origin. It is known that the inorganic
composition of the projectile is usually lead, or lead with antimony added as a
hardener[2,4,5,9].

The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
Shiona Croft

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1.2.3

The Propellant

The most important part of the ammunition in relation to analysis is the propellant.
The propellant occupies considerable space inside the cartridge case and contains
various compounds. For 0.22 calibre ammunitions, smokeless powders are the

propellant of choice[1]. These powders come in two varieties, single and double
based. Single based powders are those that contain nitrocellulose (NC) as the main
explosive material whereas double based powders contain both NC and nitroglycerine (NG). The addition of NG increases the hydrophobic tendencies of the
powder, raises the energy content and softens the powder. The stabilizers ethyl and
methyl centralite behave in a chemically similar way however, only one compound is
used in the ammunition make up, never both. The role of these compounds is to
remove oxides formed by the decomposition of NG and NC. If these oxides are not
removed, they behave as catalysts and are involved in further decomposition, which
will shorten the shelf life of the ammunition. It has also been stated that self-ignition
may occur from the increased degradation due to the auto-catalysis[10-17] of the
ammunition. Ethyl centralite (EC) removes oxides by acting as a weak base and
reacts with the decomposition products to form nitro and nitroso derivates.
Diphenylamine (DPA) is another stabilizer commonly seen in single based powders.
Its usual concentration is only 1% and it is common to see both EC and DPA in
ammunition types. Its function is similar to that of EC, as its main function is to
absorb the free nitrates that have derived from the nitrocellulose. Its degradation and
the subsequent derivatives that are formed will be discussed later in the chapter.

Plasticizers are also found in propellants and work to convert NC from its natural
fibrous state into a gel state. Dibutyl phthalate, diethyl phthalate, dioctyl phthalate,
and glycerol triacetate are common plasticizers found in ammunition today[9,18].
These compounds can also function as burning modifiers which reduce the initial
burning rate of the propellant grains and increase pressure and efficiency[19].

1.2.4

The Primer

The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
Shiona Croft

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Most primers have explosive and oxidizing properties. Many of the compounds
found in primers can be multi or mono functional. Organic compounds with nitro
functional groups are often used as primers. Such compounds include Trinitrotoluene
(TNT) or derivatives thereof. In addition to these organic compounds mentioned,
primers are also comprised of inorganic elements such as barium, lead and antimony.
These elements play key roles; for instance, an initiator (lead styphnate), an oxidiser
(barium nitrate) and a fuel source (antimony sulphide)[2,5,9,18,20].

The primer is ignited when hit by the firing pin of the weapon which results in hot
gases and temperatures being created. The ignited primer now decomposes and the
enormous pressure and energy build up consequently causes the projectile to be
expelled from the chamber of the firearm. Lead, Antimony and barium are converted
into a gas during this process which in turn condenses into tiny spheres or droplets of
residue. These spheres can range in size from 0.5 to 10 microns, making them a
valuable tool in forensic science.



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The use of Gas Chromatography-Mass Spectrometry (GC-MS) as a method for
analysing organic compounds in the forensic field is well established in areas such as
drug analysis, which suggests it could be extended to GSR research. Aebi et al[21]
has stated that GC coupled with dual MS and a Nitrogen-Phosphorous Detector

(NPD) is a powerful tool for forensic analysis. Their study concentrated on
identifying masked pharmacologically active compounds via this method and noting
its advantages over other detection systems. However, they observed that not all
pharmacologically active compounds contain nitrogen and phosphorous. Their
LQYHVWLJDWLRQ RI  – tetrahydrocannabinol and its metabolites (THC acid) show this.
This compound is the active component in marijuana or cannabis, is non volatile and
therefore Liquid Chromatography (LC) is often used to establish the concentration of
THC in a particular sample. The reason for this is because with higher temperatures
often used within a GC system, THC acid is decarboxylated to THC. This
subsequently results in an inaccurate estimation of the total concentration of THC in
The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
Shiona Croft

4


the sample. This is of significance as a small amount of THC acid decarboxylating to
THC in this process has a dramatic effect on the amount of THC detected. In their
study, while not covering a large number of compounds, did show the possible
advantages of using GC-MS in organic studies of this nature. GC allows for rapid
and sensitive separation of compounds while MS provides identification of the
resulting peaks from the chromatogram. By using mass spectral libraries, unknown
substances can usually be identified. This in turn has allowed GC-MS to be a
valuable tool in forensic analysis and will continue to do so in the future, with many
studies utilising this analytical technique[22-25].

Within the field of unfired propellant analysis, the organic compounds used for
identification have not changed significantly over the years, however, major
discrepancies exist over which of these organic compounds are totally ‘unique’ to
smokeless powders.

Mach undertook two studies in 1977[26] and 1978[27] of 33 different kinds of
ammunition to determine the feasibility of identifying gunshot residue via its organic
constituents using GC-MS. From their earlier study[26] they were not able to predict
the composition of the powder just by its brand and type. Their later study[27] agreed
with Wu et al[28,29] that the main characteristic compound is ethyl centralite but it
is present in comparatively small amounts. Mach’s work did not extend to
discriminating different batches of ammunition. Their main focus was on comparing
the unburnt particles to burnt ones. The results indicated the components detected
were of varying concentrations. It could have been useful, therefore, to establish a
database of the concentrations of the various components detected. Unknown
samples could have been compared to this database to establish whether it had
similar properties to the samples of known origin in the database (i.e. a profiling
method). Interestingly, their results showed that diphenylamine was the most
common additive, and while this is not a new discovery, the lack of investigation into
other organic compounds in the samples would indicate their method is in need of
further exploration. Dibutyl phthalate was seen in about half of their samples but
nitro-glycerine was seen in a substantial number of samples, which suggests that
their work was paving the way for further investigations into this area.
The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
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Wu et al[29] used a tandem mass spectrometry system (MS-MS) to show that the
organic components of GSR are more characteristic than their inorganic counterparts.
MS-MS has the added advantage of being more selective in that molecular ions are
separated by the first mass spectrometer, and these subsequent selected ions are
reanalysed by a second mass spectrometer to give a more specific pattern. It was

stated that the main components of the gunshot residue are NG, trinitrotoluene
(TNT), 2, 4-dinitrotoluene (DNT), DPA and methyl centralite (MC). In their research
they were able to separate the main components of the gunshot residue by High
Performance Liquid Chromatography (HPLC) and observe the molecular ions of the
main stabilizer methyl centralite, which are said to be the most characteristic
compounds of gunshot residue[28]. The components were analysed by HPLC-MS
and the compounds eluted in the following order (table 1.1):
Table 1.1: Elution order for constituents using HPLC-MS[29]

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This table is not available online.
Please consult the hardcopy thesis
available from the QUT Library
When the compounds were then subjected to MS, characteristic ions were seen. This
however, was done using negative ion mass spectrometry which is not the usual
methodology. The Molecular ion (M-H)- at m/z 226 was seen with fragmentation
ions: (M-HNO3)- at m/z 163 and (NO3)- at m/z 62. These ions are said to be
characteristic of NG[29]. The characteristic molecular ion of MC was seen at m/z
241 and the fragmentation ions at m/z 134, 106, 77, 51. While it has been suggested
that the various components of the smokeless powder do have other origins, MC and
EC are thought to be characteristic of smokeless powders especially when seen with
NG[28]. These two compounds are uncommon in other industries. NC, on the other
hand, is used in lacquers, varnishes, printing and in the pharmaceutical industries
while DPA is used in rubber preparations and in the food industry. NG has uses in
the explosive and pharmaceutical industries[28].

The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
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6


Wu et al [29] did however suggest that by focusing their studies on methyl centralite
and using concentrated sample volumes, the level of contamination of the injector
contributed to lower than expected detection levels. Several cleaning methods did not
help the situation and so, they adopted a 100 fold dilution of the samples with
methanol to avoid further contamination. Once this method was adopted, they were
able to successfully discriminate 10 persons who had recently fired a revolver, from
10 persons who had not fired a gun. Further experiments could adequately identify
MC on a person who had fired a pistol eight hours earlier and on the hand of an
individual who had washed their hands after firing a pistol. Both tests showed a
positive correlation and they argued that their work could be used in criminal
investigations when an offender managed to escape after firing a firearm, but was
caught several hours later. They proposed that even if the offender washed their
hands with water, detectable amounts of MC could be identified using this method.
This method was found to be sensitive and selective when using Multiple Reaction
Monitoring (MRM) mode, which used ions of m/z 241 as precursor ions and ions of
m/z 134 as product ions, and while their method mainly focused on methyl centralite,
it could be adapted to identify other components, and therefore is a promising
technique.

While Wu et al [29] concentrated on MC as the most characteristic compound for the
identification of smokeless powders; DPA and its derivates have received wide
attention. It is known to decompose substantially[10-17,30-35] and Tong et al[17]
suggested that the ‘detection of DPA may be taken as evidence’ as many gun
powders do not contain the stabilizers methyl or ethyl centralite. However, it should
be noted that DPA is also found in the rubber and food industry.

[2-nitro-DPA]

[DPA]

[N-nitroso-DPA]
[4-nitro-DPA]

Figure 1.2 Degradation of DPA [10,11]

The Analysis of Unfired Propellant Particles by Gas Chromatography-Mass Spectrometry: A Forensic Approach
Shiona Croft

7


Bergens and Danielsson[10,11] investigated the degradation mechanism of DPA and
their results are shown above in figure 1.2, however, this is in contradiction to the
report of Lussier[14] who suggested other reaction mechanisms. Bergens and
Danielsson concentrated on monitoring the DPA at a temperature of 85ÛC to note the
breakdown products achieved. The conclusion was after analysis by LC, only a small
percentage of the DPA is converted to 2-nitro-DPA and 4-nitro-DPA. Conversely, Nnitroso DPA corresponds to the largest breakdown product produced, which in turn is
responsible for further interaction with the NC degradation products. After 15 days
of storage at this temperature, the concentration of the 4-nitro-DPA is about twice as
much as 2-nitro-DPA which is supported by the work by Lussier and Gagnon[14].
The concentration-time curves further support the idea that the DPA is rapidly
degraded into these products when introduced to a NC matrix.

Concentration anomalies of DPA were observed in another study[14] which
encountered difficulties during extraction stages; however in the study, critical
evaluation of their extraction and solvent techniques have rendered the paper quite
useful. The cause of the significant DPA loss was not fully explained, and while it is

of extreme importance to understand the chemistry of the reactions, the authors have
suggested that the interaction between the NC matrix and DPA has produced a
compound not amenable to extraction techniques. Methylene chloride was used
suggesting that most of the NC matrix should have been removed during the
extraction stage. It does then beg the question of what DPA is reacting with to create
degradation products. The authors gave many possible explanations including the
interaction with nitrate esters, causing cleavage to leave alkoxy radicals, which are
said to be responsible for rupture of the cellulose chain. Furthermore, the NC-DPA
structure that is then formed could react with nitrous oxides and N-nitroso-DPA, with
2 and 4-nitro-DPA possibly being by-products of this interaction. In part 2 of the
study[10] it was suggested that spectroscopic techniques be employed to determine
whether or not the DPA has been incorporated into the NC matrix. While more
complex reasons were suggested for the DPA degradation, it is important to note the
possible interaction with oxygen as a degradation source[11]. The authors did not
give reasons behind the reaction between DPA and oxygen nor its interaction with

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light. It may be worth investigating these two physical properties on the
decomposition of DPA.

Mathis et al [36] further highlighted the importance of developing an analytical tool
for the characterisation of GSR. Their study involved seven compounds; DPA, Nnitroso-DPA, MC, EC, dimethylphalate, diethylphthalate and dibutylphthalate
(DBPH). Mathis et al understood the necessity of producing a chemical profile that
allows for determination of distinguishable characteristics. While they acknowledged
the use of GC as a tool for the analysis of GSR, the study involved the use of

gradient reversed phase liquid chromatography as it was felt that the nitro
compounds were susceptible to thermal degradation by GC-MS. This contrasts with
the work of Burns et al[22] who used GC-MS to analyse and characterise NG based
explosives. Burns et al successfully identified nitro esters and nitro aromatic
compounds from the samples and undertook the important task of examining any
batch-to-batch differences between commercial explosives. Determination of the
sample’s total DNT content allowed for further discrimination of the ammunition
type. This information was compared to the manufacturer’s specifications, which
enabled the explosive batch number to be established.

Despite the contradiction, Mathis et al were able to quantify several organic
constituents such as centralites, phthalates and diphenylamine by gradient reversed
phase LC. This phase was chosen due to the spread in polarities of the main
constituents. Coupled with MS, this technique is very powerful in both separating
and identifying capabilities. The separation method was further developed by
Wissinger et al in 2002[37] however slight changes were made to accommodate
Mathis’ study. Ammonium acetate (CH3COONH4) was used to assist the ionisation
process. Methylene chloride as a an extraction solvent was also used as its
application is well documented in OGSR[10,11,25,37]. Its role is to keep the NG
insoluble, which enables ease of removal upon reconstitution. The LC conditions
were modified compared to those used by Wissinger by using a lower flow rate,
smaller column and by adding ammonium acetate to the mobile phase to help in the
ionization stage. The study was significant to GSR analysis as it successfully
discriminated characteristic organic compounds; however, the ambiguity of the
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conclusions reduces the overall value of the work. Wissinger did comment on the
power of GC-MS, particularly with respect to the analysis of phthalates which may
have been missed by LC-MS.

In 1989, Keto et al[18] compared smokeless powders using Pyrolysis Capillary Gas
Chromatography. This method was chosen since there is no sample preparation
involved and consequently any error associated is eliminated. The authors also
argued that by using the capillary column, the better separation would increase the
analytical benefit. Meng et al [20]agreed with this statement by saying that the
‘separating power of the capillary column in the GC is unparalleled’. However, by
using statistical measurements, the amount of detectable difference between
manufacturers was shown to be very small, rendering this method limited in source
identification. This is a situation where the use of MS could be of significance to
properly identify the peaks in the chromatogram. While no real differences seen
between different manufacturers, close examination of the results showed different
levels of peak intensity, which was not appropriately recognised in the paper. The
size of the study was limited to only three samples: Hercules Red Dot; WinchesterWestern 540; and Dupont Hi-Skor 700x brands. This factor could be the reason for
their poor results. Many brands and types of ammunition should have been included,
especially when their statistical method of validation is a chemometric method,
which requires a large sample population.

In a survey of GSR analysis by Meng et al[9], efforts were made to compare the
various techniques available for the study of GSR. They incorporated both inorganic
and organic analysis. From this report, it is clear that there is a variety of techniques
available for analysis of the organic components, whereas in inorganic analysis there
are only four main instruments of choice: Atomic Absorption Spectrometry (AAS);
Anodic Stripping Voltammetry (ASV); Neutron Activation analysis (NAA); and
Scanning Electron Microscopy coupled with the Energy Dispersive X-Ray detector
(SEM/EDX). When analysing the organic components, there is a greater variety of
methods to choose from. Such techniques include Thin Layer Chromatography

(TLC); Gas Chromatography (GC); Infrared Spectroscopy (IR); High Performance
Liquid Chromatography (HPLC); Mass Spectrometry (MS); Fluorometric detection;
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Supercritical Fluid Chromatography (SFC) and Capillary Electrophoresis (CE). The
use of Raman Microscopy has also been noted in Organic GSR analysis[38]. More
recently, the use of time-of-flight secondary ion mass spectrometry (TOF-SIMS) has
been noted in the study and characterisation of propellant samples[39,40]. This
analytical technique has the advantage of obtaining elemental and molecular
information from surface samples with a particularly low level of detection. It can
also capture molecular images which may be useful for investigating distribution of
additives and explosives constituents of the powder.

TLC has the advantage of being simple, rapid, moderately sensitive and relatively
cheap. However, it has poor quantification capabilities and requires a large amount
of sample. Infrared Spectroscopy (IR) has been successfully used to determine the
presence of nitrocellulose in samples[41]. However, it was not as successful in
determining the other minor components present at low concentration, but which are
equally important in function. Such components include the stabilizers in the
propellant grains, which may be used as characteristic compounds of GSR.
Furthermore, the fact that only NC (not being totally unique to GSR) was accurately
detected in this study may render this technique unsuitable for the analysis of GSR,
as there are many other vital components, which have been overlooked. It may be
useful for the confirmation of substances when a positive result using another
method such as HPLC, has been obtained.

HPLC can be used for the analysis of organic compounds and has the added
advantage of being able to separate ionic compounds, polymeric materials and polyfunctional compounds of high molecular weight. Also, HPLC is not limited by
thermal stability of the compounds. Due to the higher temperatures in the GC
instrument, some compounds cannot be adequately analysed as they may undergo
decomposition during injection.

The MS system is a highly specific and sensitive method and has previously been
shown to be a powerful tool in analysing explosive compound[28,29]. Mass
Spectrometry is an excellent analytical system which is best coupled with the GC or
HPLC systems to give both separation and identification of the compounds in a
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mixture. It has been proposed that the coupling of MS with GC will render the best
results since both operate in the gaseous phase and the separated components can
sequentially flow to the MS detector where the individual mass spectra can be
obtained[21]. Most investigations into the organic compounds of GSR have coupled
the MS with HPLC but the use of GC is equally as valid.

Fluorometric detection has been noted as a sensitive and selective mode of detecting
organic components when using HPLC. Meng et al[20] in 1996 investigated the
detection of ethyl centralite and 2-4 DNT in GSR after derivatisation with 9fluorenylmethylchlorformate. Their method used a fluorometric detection which they
claimed to be a more sensitive and selective method for the detection of organic
GSR. EC was first hydrolysed to N-ethylaniline (NEA), which was further
derivatised with dansyl chloride (DNS-Cl). The end product was a fluorescent
compound that could be separated using TLC or reversed phase HPLC. While the
authors claim that fluorometric detection is sensitive and selective, their analysis

revealed that only three out of eleven kinds of ammunition contained EC. They
analysed three other compounds recommended as characteristic compounds[35].
These were 2,4 DNT, 2–nitro diphenylamine, and 4–nitro diphenylamine. It is
suggested that they can be reduced to their aromatic amines which then allows for
derivatisation using the labelling agents such as 9-fluorenylmethylchloroformate
(FMOC). Interestingly, the use of diphenylamine derivatives is in complete
contradiction to their previous statement in 1994[42] where they stated that, ‘DPA
has been regarded as an evidentially irrelevant compound’. The authors were able to
achieve good detection levels (1 pg levels) which is lower than their previous
detection limits of 60pg using DNS-Cl[42]. However, only six out of eleven samples
were shown to contain EC or 2, 4-DNT or a combination thereof. Their method
failed to detect the other two compounds previously mentioned to be more
characteristic than EC and DNT. The authors suggested that while the method may
be sensitive, further analysis of the reduction, hydrolysis, derivatisation and
fluorescent steps could ultimately improve the technique.

The use of Supercritical Fluid Chromatography (SFC) has not been extensive in the
area of organic gunshot residue analysis; however it has been reported that its
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application is suitable for thermally labile or non-volatile substances. An advantage
of SFC is that it is compatible with virtually all detectors used in established
chromatographic techniques such as GC and HPLC. In a study by Munder et al,
smokeless powders were analysed using this technique and while they were able to
detect several minor constituents such as ethyl centralite, diphenylamine,
dinitrotoluenes and dibutyl phthalate, they were not able to distinguish between

different brands. The possibility then of classifying smokeless powders by
manufacturer using this technique is low.

An interesting example of characterising black powders is the study by MacCrehan
et al in 2002[43] who looked at associating gun powders and residues by
compositional analysis. They identified the main constituents of the powder to be
nitrocellulose, nitro-glycerine, diphenylamine and ethyl centralite. Characterisation
of the ammunition type was achieved by calculating a propellant to stabiliser ratio
(P/S ratio) developed by Reardon et al which is a simple method to use and interpret.
The study collected 7 brands with only 50 rounds in each. Each of the cartridges
were assigned numbers from 1 – 50 and the, numbers 1, 10, 20, 30, 40, 50 were
assigned codes. The powder was removed from the cartridge and placed in a vial
which could only be traced back to this code. This method then allowed for a random
choice for the order of analysis. Ultrasonic Solvent Extraction/Capillary
Electrophoresis was their method of choice and while it was adequate for detection
of certain compounds, some brands were shown to contain diphenylamine only. This
observation is unusual as powders are comprised of various substances such as
propellants, hardeners, stabilisers and so on and therefore detection of these would be
expected. To fully appreciate the characteristic associations, a more sensitive and
selective analytical procedure should be adopted so that a characteristic profile for
each cartridge could have been developed. Furthermore, as suggested by Smith et
al[44], electrophoresis should only be a complementary tool as results can vary
according to different parameters. The study however shows promise in selectivity
and sensitivity but compared to other analytical techniques, it appears that this
method is somewhat lacking. MacCrehan’s study is an example however, of how
important it is to characterise and discriminate powders from each other. This can

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only be of benefit for investigating authorities who rely on validated databases with
which to compare their unknown samples.

Furthermore, in an important recent study by MacCrehan[45] an attempt was made to
create a smokeless powder reference material for laboratories undertaking explosive
and propellant analysis. The aim was to characterise the organic additives commonly
found in smokeless powders such as nitroglycerin, ethyl centralite, diphenylamine
and the nitration product N-nitrosodiphenylamine. This would be achieved using the
analytical

techniques

Micellar

capillary electrophoresis

(CE)

and

Liquid

Chromatography (LC). Three candidate smokeless powders were studied. Powder 1
was Hi Skor 700X (an NG containing powder stabilized with EC). Powder 2 was
Winchester 231 (an NG powder stabilized with DPA) and handgun reloading
smokeless powders purchased from a local gun shop. Powders 1 and 2 became the
inter laboratory comparisons of smokeless powders analysis and measurement and

interestingly, MacCrehan noted a number of inconsistencies from the 20 participants.
Many laboratories reported surprising results with some identifying EC in powder 2
which was stabilized by DPA. They report that manufacturers often use recycled
surplus of materials and this material may have different compositions than intended.
These trace compounds and inhomogeneity of the propellant lead to uncertainty of
the true make up and chemical composition of the smokeless powder. For this
reason, the commercial powders were deemed unsuitable for reference materials.
However, the use of Powder 3 (the handgun reloading smokeless powder) was
explored and through a series of experiments and involving thermal stability and
homogeneity, it was deemed that Powder 3 was suitable for reference materials with
the use of LC. The testing revealed that storage at room temperature or below was
acceptable and sampling sizes should be 20 mg or greater. These conclusions were
supported by the fact that relative uncertainties for the additives were much smaller
with room temperature stored samples and of sizes 20mg or greater. The study was
able to provide a reference material from Powder 3 with a level of uncertainty <5%.
As this is a relatively new study, further follow up inter laboratory analysis and
testing should be carried out to support the long term use of such reference material.

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