Elemental Analysis of Unburned Matches by SEM/EDS for Forensic Comparison
1
Allen ,
2
Neff ,
1
Rushton
Lance
David
Catherine G.
1Forensic Science Program and 2Chemistry Department, Marshall University, Huntington, West Virginia
Introduction
Matches can be found at a variety of crime scenes:
arsons, bombings, clandestine labs, and so forth. A
technique capable of comparing a match found at a
crime scene to a book of matches found in a suspect’s
possession would be valuable in associating the
suspect to the crime scene.
Andrasko1 used SEM/EDS to identify burned
matches, and Dixon2 used the fibers in book matches
to identify a match originating from a specific book.
SEM/EDS analysis has also been used to analyze
unburned matches, but not to distinguish one producer
from another.
Materials and methods
Preparation Method 2
A razor blade was used to remove the entire match
head from a match. The match head was ground with
a mortar and pestle to homogenize the sample. This
sample was placed between two glass microtome
blades and pressed flat with a minimum pressure of 50
psi. Samples from five different matches of the same
book were prepared for two of the match producers.
Results
A spectrum was collected from five matches from each
book for all seven match producer (ex. A1a ─ Ale). The
major elements in all the matches were the same (silicon,
sulfur, chlorine, and potassium), But spectra were visibly
different based on relative amounts of major and trace
elements.
SEM/EDS Parameters
A JEOL 5310 LV scanning electron microscope with
an Oxford Pentafet electron dispersive spectrometer
detector with thin beryllium window and ISIS analysis
package was used. The settings used were: 300 mtorr
low vacuum, 25 keV acceleration voltage, 24 mm
working distance, and 109 mAmps condenser lens
current (spot size). To ensure the spectra reflected the
real composition of the matches and not just a few
particles in the match, a magnification of 350x was
used. A live time of 300 seconds was used as the
collection time of each sample.
Figure 5. Dendrogram of the PCA analysis of samples
prepared by method 2.
Figure 2. Dendrogram of the PCA analysis. Shows the
amount of dissimilarity between the samples.
A large amount of variation can be seen in each
set of match samples, thus not allowing for
differentiation between one producer and another.
Sample preparation method 2 was devised to improve
uniformity of the sample, and reduce variation. Sample
preparation method 2 was used to prepare more
samples for U1 and L1. U1 was chosen because there
was a large variability in the samples. L1 was chosen
because the sample were similar to U1. It was hoped
using preparation method 2 the U1 samples would
have less variation and be distinct from the L1 samples.
Sample Preparation
Matches produced by seven different match
companies were analyzed. A list of the companies
along with the samples corresponding to those match
producers can be seen in Table 1. The samples were
prepared by two methods. The second method
produced a more homogenous sample.
Preparation Method 1
A razor blade was used to cut a flake of the match
head from the match. This flake was then placed
between two microtome blades and pressed flat with a
minimum pressure of 50 psi. Samples from five
different matches of the same book were prepared for
all seven match producers.
Figure 3. Lion Match Company sample (L1b) prepared
by a flake of the match head cut off and pressed flat.
Although the variation in each of the two sets
(U1 and L1) decreased, the U1 samples still were not
distinct from the L1 samples. This suggests
reanalysis of all samples after being prepared by
method 2 would reduce the variability in each set.
Conclusions
The spectra of some matches showed a visible
difference in the amount and types of elements.
These differences ranged from large variability in the
amount of major elements to the presence or absence
of trace elements. Even with the visible differences in
many spectra, the variation in each match producer
set made comparisons impossible.
With the second method of sample preparation the
particle size was significantly smaller. Thus, the
homogeneity was improved and variations within a set
reduced. While it has been shown that even with the
second preparation method some matches are not
distinct from others, groups of certain match producers
may be distinct from other groups of match producers.
Future work would include preparation of sample
for the other five match producers using the second
preparation method. These could then be analyzed by
the SEM/EDS. The PCA analysis would then show if
groups of match producers differ from other groups.
Literature cited
Andrasko, J. Identification of Burnt Matches by
Scanning Electron Microscopy. J. Forensic Sci.
1978, 23, 637-642.
Table 1.
Match Producers
Samples
Atlas Match
A1a ─ A1e
Atlantis Match
AT1a ─ AT1e
DDBean & Sons
DDB1a ─ DDB1e
Diamond Match Company
D1a ─ D1e
Lion Match Corporation
L1a ─ L1j
Ohio Match Company
O1a ─ O1e
Universal Match Corporation
U1a ─ U1j
Dixon, K.C. Positive Identification of Torn Burned
Matches with Emphasis on Crosscut and Torn Fiber
Comparisons. J. Forensic Sci. 1983, 28, 351-359.
Figure 4. Lion Match Company sample (Lig) prepared
by entire match head being ground and pressed flat.
Figure 1. Spectra of A1b, D1d, and L1e. Elements present are
similar, but relative abundance differs.
Energy windows were used to calculate the integral
values of eleven different elements. Relative abundance
ratios were calculated from the integrals of each element
in relation to potassium. These ratios were compared by
Principle Component Analysis (PCA).
Acknowledgments
The particle size is much smaller in the sample
ground with mortar and pestle (method 2), figure 4,
than in the sample prepared by method 1, figure3. The
ratios for the samples prepare by method 2 were used
for more PCA analysis.
The authors would like to thank Dr Michael Norton
for providing accessible and well equipped
microscopy facilities, supported in part by NFS
COBRE grant (period 2004-2009). We also
appreciate the help of Dr. Graham Rankin with the
PCA analysis and Dennis Ward with guidance on
sample preparation.