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Z. Kristallogr. Suppl. 23 (2006) 35-40
© by Oldenbourg Wissenschaftsverlag, München
Application of X-ray diffraction in
forensic science
Marek Kotrlý
Institute of Criminalistics Prague, Strojnicka 27, P.Box 62/KUP, 170 82 Prague 7,
Czech Republic
Contact author; e-mail: [email protected]
Keywords: forensic science, powder diffraction, phase analysis
Abstract. XRD analysis is not an extremely popular technique within forensic science community. It has been used in this field for many years, but only in a few specialized laboratories around the world. Its popularity as an analytical technique in this area has been fluctuating over last thirty years.
Standard methodology of XRD was modified and optimized for small amounts of samples.
As a results it is possible to work with 10-6 g of a sample. Currently, XRD analysis is employed in soil analyses, analyses of explosives and post blast residues, pigment and paints
analyses, goods identification, analyses of unknown substances, plastics and polymers, alloys
and metals, identification of degraded bones and drug analyses.
Introduction
XRD analysis is not an extremely popular technique within forensic science community [1].
It has been used in this field for many years, but only in a few specialized laboratories
around the world (e.g. FBI (USA), BKA (Germany), FSS (England), NFI (Netherlands),
central laboratories in Poland, Ukraine and Russia, laboratories in Japan and Australia). Its
popularity as an analytical technique in this area has been fluctuating over last thirty years.
This could be ascribed to the transition from photographic to diffractometric methods, and
from manual interpretation to identification via electronic databases, which has been relatively slow over the past three decades.
XRD analysis started to be employed at the Institute of Criminalistics Prague (ICP) in the
60s of the past century for identifying short-circuit products on copper conductors. In the 90s
there was a lab with two goniometers in classic Bragg-Brentano reflexion geometry and with
another radiation source, which is utilized for Guinier and Gandolfi cameras with a classic
film. Film carriers from these chambers are subsequently digitalized and evaluated as records
from both goniometers. ICDD database and client databases are used for evaluation.
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European Powder Diffraction Conference, EPDIC 9
Methodology
In forensic field is necessary to work with small amounts of samples. Goniometer was modified for monocrystal Si cuvette in orientation parallel with plane 432. As the second step
primary geometry of goniometer (position and size of slits, Soller slits and monochromators)
was tested, step size factor and exposition time for gaining optimal pulse statistic for distinction of poor diffractions. For processing low-quality records PC programs ZDS and Bede
ZDS for Search/Match are used. Diffraction peak position is determined by the third and
fourth derivatives. Searching for up to ten phases in the mixture with the high differentiate
process algorithm is possible [2].
As a result it is possible to work with 10-6 g of a sample.
The importance of XRD and phase analysis in forensic science lies namely in:
• the possibility of analysis of quite small-volume samples [3]
• the method is relatively non-destructive (the sample can be used for further analyses
even after possible powdering) it follows from the mentioned fact that probative
value of the material is preserved
• the method allows exact identification of phases in a mixture (unlike other instrumental chemical methods)
• in majority of cases it is possible to determine quantity (or semiquantity) of substance in a mixture
• the method is conclusive for potential court proceedings
Currently, XRD analysis is employed at ICP in 7 main areas:
Soil analyses
In complex analyses and soil comparisons the method is indispensable for determination of
clay fraction. Other available analytical methods (EDS/WDS, XRF, FTIR, etc.) are not capable of performing exact determination of phases, namely alumosilicates. Our own calibration
sets are used for semiquantitative XRD analysis (figure 1).
Explosives and post blast residues
With determination of explosives and post-blast residues, direct determination of inorganic
and organic phases of explosives and post-blast residues (following the sampling of the postblast scene and possible separations and concentrations of the material) is used. XRD methods are used also for evaluation of the effect of separation and concentration methods of
post-blast residues during their testing. The post-blast scene is usually very difficult to analyse, since there are particles of all kinds of materials destroyed by the explosion, in which
there are relics of post-blast residues dispersed all over, often below the detection limits.
That is why different concentration and separation procedures capable of reducing the content of contaminants are used. During tests of effect of these methods, phase XRD analysis
with semiquantitative evaluation proved the most convenient.
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Z. Kristallogr. Suppl. 23 (2006)
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Figure 1. Block diagram of forensic soil analysis
Pigments and paints analyses
Pigments and paints analyses XRD methods are used in complex expert examination during
determination of phases of artworks (paintings, sculptures etc.), car paints (analyses of abrasions and fragments after traffic accidents), analysis and comparison of lacquer systems of
tools and instruments, lacquer systems used in building industry and some analyses of printing colours and paints (figure 2).
Examination of pigments of artworks is requested for solving the following issues:
•
•
•
partial examination to determine the age of the painting (on the basis of used pigments, canvas type etc.)
confirmation of originality of adjustments of the paintings, or affiliation of the
painting and the frame (e.g. confirmation that the pictures were in original frames
prior to the theft)
distinguishing the original from forgery (the most complex expert examinations, in
which an expert from the National Gallery participates) [4]
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One of the revolutionary types of pigments is so called ”effect”, plate-like, or colour-variable
pigments. These pigments are based on small metallic or dielectric particles covered by one
or more layers of oxides and fixed in a transparent layer. Depending on the angle of incident
light, the proportions between reflected and absorbed beams are changing, total reflections
and interference occur. The result is a completely different colour perception from different
angles (e.g. dark green - orange). Forensic identification and comparison of colour variable
pigments (the size of the particles - X - X00 micrometers and thickness of the wrapping
layers in X - X00 nm) present complex process, which includes methods like light microscopy in transmitted light and polarization, reflected light and polarization, electron microscopy, EDS and XRD analyses, FTIR etc [5].
Figure 2. Block diagram of complex forensic identification and comparison of colour variable pigments.
Goods identification
Identification of type and origin of goods customs and financial frauds, counterfeiting of
original branded products, money laundering. XRD methods belong to the complex of methods used for determination of the exact type of goods or material (e.g. materials for semiconductor components, fertilizers and pesticides, special heat-resistant materials, precious
stones, etc.)
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Unknown substances analyses
Identification of unknown substances, potential poisons and contaminants - these analyses
are requested for complex analyses of materials that can harm the environment or are subject
to special treatment (industrial accidents and leakage of dangerous substances (figure 3),
attempts to dispose of these substances on ordinary waste dumps, threatening and extortionate letters currently frequent packets with unknown white powder etc.). For these types of
analyses it is necessary to use special user databases comprising standards of poisons and
substances, which are not included in common commercial databases.
Figure 3. Identification of white powder from the threatening letter (from the “anthrax” period), picture from optical microscope.
Degraded bones
Confirmation of degraded skeletal discovery, burnt, fragments damaged or unusual to such
extent that anthropologists require confirmation of composition. In this sphere, it is used for
confirmation of phases, present in bone construction (figure 4).
Drugs
Quantitative drug analyses - with the aid of powder diffraction it is possible to reach higher
precision of quantitative analysis of some narcotic mixtures than with instrumental methods
of organic analysis (FTIR, GC). XRD analysis is in many cases faster and sample preparation is simpler. Internal standard is used for quantitative analysis.
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European Powder Diffraction Conference, EPDIC 9
Figure 4. Comparison of two spectra of bones: A is recent, relevant relic of bone after a fire; B is relic
from fossil bone (picture from optical microscope and SEM-BSE).
Further development of XRD methods in forensic science will be perhaps brought by capillary optics and its application in micro diffraction, which even today allows execution of
non-destructive analysis from point sized under 100 micrometers.
References
1.
2.
3.
4.
5.
Thatcher, P.J. & Briner, G.P., 1986, Powder Diffraction, 1, pp.320-324.
Ondrus, P., 2003, Materials Structure, 10, No 1a, pp. 22-24.
Rendle, D.F., 2003, The Rigaku Journal, 19/No.2 & 20/No.1, pp. 11-22.
Kotrly, M. & Turkova, I., 2003, Forensic Science International, 136, supl. 1, p. 357.
Kotrly, M., 2003, Forensic Science International, 136, supl. 1, pp. 356-357.
Acknowledgements. XRD methods at Institute of Criminalistics Prague was supported by
grant-aided projects of the Czech Republic Ministry of Interior MVCR RN 19961997008,
MVCR RN 19982000005.
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