Transcript The Bali Bombings of 2002

THE BALI BOMBINGS OF 2002
Jenessa Dilley
Ryan Simpson
Adrian Smalley
A NOTE ON STATISTICS
•
Statistics in the form of analysis of variance helps to reveal the underlying causes of poor
precision. Even more important is to reveal a weakness in the trueness. The aim of any
chemical analysis is to determine the true value of the sample to achieve accuracy. It
would be that we measure extremely precisely, that is, we observe a very low variance.
That does not mean that we have determined the true value for the sample. Perhaps, we
made a mistake during sample preparation. If only a single sample is prepared, the
sample preparation error is an error in the trueness. Therefore, it is necessary to process
several subsamples to obtain a representative estimate of the true value of an analyte.
•
The error in trueness is the difference between the measured value and the true value for
the sample
•
A single measurement value never reveals a random error, and a single incorrectly
functioning measurement can never reveal a lack in trueness
•
Measuring small concentrations will generally result in large variance
• To check accuracy we therefore have to carry out multiple error-dependent steps on
the way to the final result
ORTHOGONAL TESTING (REPRODUCIBILITY)
•
A satisfactory level of confidence in establishing the identity of a questioned sample is
generally achieved after corroboration from two independent techniques
• This is known as orthogonal testing
• The level of confidence rises with each positive result
•
Orthogonal testing is relatively easy to achieve when dealing with bulk material
• It is more difficult when dealing with trace quantities, especially those from an
inorganic source which may occur naturally in the environment, or if they are volatile
and unlikely to persist in the area
•
“Time of flight mass spectrometry can get past the problem of thermal instability by
performing very rapid analyses using a short narrow bore column, and de-convoluting the
resulting chromatogram by exceedingly rapid mass spectral analysis. This however raises
the question as to whether it is truly orthogonal testing for if the chromatography does not
resolve co-eluting compounds, then is it really only the one technique?“
METHODS & TECHNIQUES
•
The following slides highlight the methods and techniques used in the analysis of the Bali
Bombing of 2002
•
Some of the errors associated with the experiments may be increased if the following
practices are not implemented
• Careful technique (accuracy)
• Setting experimental parameters
• Controlling the environment
• Following standard operating procedures
• Reducing sample exposure to contaminants
• Etc.
THIN LAYER CHROMATOGRAPHY (TLC)
• All chromatographic techniques flow the mixture, that
is to be separated, through a material that retains
some components more than others
• Different compounds in the sample mixture travel
at different rates due to the difference in their
attraction to the stationary phase, and due to their
differences in solubility in the solvent
• This causes different components to flow through
the material at different speeds, so they separate
• TLC was used to test for organic explosives
• Ex. TNT, RDX, PETN
THIN LAYER CHROMATOGRAPHY (TLC)
•
Limitations:
• Low resolution susceptible to contamination
• Open system, can contribute to the statistical error
• The spotted plate is normally dried before development.
• The drying step can be a big, unpredictable source of error. If too much heat is
used, spots can remain at the start and samples or standard can be degraded
• During the drying process, the mobile phase evaporates from the upper part of a
plate and produces secondary chromatography, which is the main reason for
poor precision in TLC
• Uncontrolled separation conditions produce poor reproducibility
• Spraying with a special reagent is commonly used to allow for visualization of
components, which have no chromophore
• This technique is less reproducible than dipping of the plate, which is a strictly
empirical operation
GAS CHROMATOGRAPHY (GC)
•
GC is a common type of chromatography used in analytical chemistry for separating and
analyzing compounds that can be vaporized without decomposition
•
As the chemicals exit the end of the column, they are detected and identified
electronically. The function of the stationary phase in the column is to separate different
components, causing each one to exit the column at a different time (retention time). Other
parameters that can be used to alter the order or time of retention are the carrier gas flow
rate, column length and the temperature
•
It can be used to test the purity of a particular substance, separate the different components of
a mixture and even determine the relative amounts of such components
•
In some situations, GC may help in identifying a compound
•
Various detectors can be used some of which are sensitive to a wide range of components, and
work over a wide range of concentrations and others which are sensitive to only specific types
of substances and/or work well in narrower ranges of concentrations
•
GC was used to test for nitrogen-containing, nitro-containing and organic explosives
•
Ex. TNT, RDX
GAS CHROMATOGRAPHY (GC)
•
Limitations
• Requires volatile analytes
• Incorrect integration
• Especially false data density, false integration start and stop because of poor
peak detection, false base line positioning. There are further error sources in
quite some - even latest commercial - integration software like missing signal
size analysis and missing or poor automatic switching of data density with
growing retention time
• If the temperature is too low, substances may not elute during the time the
instrument or the detection / integration is on. This falsifies the analytical results
drastically and may damage the separation system, at least may change the polarity
or selectivity of the stationary phase.
• If the temperature is too high this may cause peak overlapping of early eluting
substances and reduce the life time of the separation system.
GAS CHROMATOGRAPHY WITH ELECTRON
CAPTURE DETECTOR (GC-ECD)
•
Refer to GC
•
An ECD is a device for detecting atoms and molecules in a
gas through the attachment of electrons via electron capture
ionization and is used in gas chromatography to detect trace
amounts of chemical compounds in a sample
•
Limitations:
• Requires volatile analytes insensitive to hydrocarbons
• ECD has a limited dynamic range and finds its greatest
application in analysis of halogenated compounds
GAS CHROMATOGRAPHY WITH THERMAL
ENERGY ANALYZER (GC-TEA)
•
Refer to GC
•
The TEA is an N-nitroso detector that is based on the catalytic cleavage of the thermally labile
N-NO bond and the subsequent detection of the nitrosyl radical by its reaction with ozone. The
TEA can be interfaced to a gas chromatograph for volatile N-nitroso compound analysis
•
Limitations:
•
Requires volatile analytes
•
Expensive
•
Limited to nitro compounds
•
Requires optimal conditions involving temperature, pressure and residence time in order to
achieve maximum sensitivity with minimum possible interference
HIGH PERFORMANCE LIQUID
CHROMATOGRAPHY WITH UV OR DA DETECTION
(HPLC-UV OR DA)
•
HPLC has higher resolution when
related to TLC
•
UV detectors measure absorption
of radiation from chromosphere’s
in eluted compounds over the
range 190-400nm
•
Limitations:
• Low selectivity
• It is not selective for
compounds if they absorb at
the same wavelength
INFRARED SPECTROSCOPY (IR)
•
IR is the spectroscopy that deals with the infrared region of the electromagnetic spectrum,
that is light with a longer wavelength and lower frequency than visible light. It covers a
range of techniques, mostly based on absorption spectroscopy.
•
Limitations:
•
Residues require separation prior to analysis
•
Looks for functional groups (ketones, alcohol, etc.) in molecules to help determine their
components and structure. Functional groups do not dictate what molecule is being
detected
•
It is used universally for organic and inorganic compounds. (Not exclusive)
• Radiation Curves: Certain bands of radiation located near the IR spectrum may not
be clearly defined and can therefore be hard to determine and analyze. This can lead
to confusion and cause overlap of the signals to give difficult results to read off of the
instrument. Due to this lots of calibration and tuning is required to set the instrument
for each individual test
MASS SPECTROSCOPY (MS)
•
MS is an analytical technique that measures
the mass-to-charge-ratio of charged particles
•
Used for determining masses of particles, for
determining the elemental composition of a
sample or molecule, and for elucidating the
chemical structures of molecules, such as
peptides and other chemical compounds
•
Limitations:
• Doesn't directly give structural
information
• Needs pure compounds
• No contamination
• Difficult with non-volatile compounds
GAS CHROMATOGRAPHY WITH MASS
SPECTROMETRY (GC-MS)
•
Refer to GC
•
Refer to MS
•
Limitations:
• Limited to volatiles
• The experimental conditions, such as temperature, pressure, carrier gas flow rates,
etc. must be identical to those used to analyze the specimen
• Due to the investigation occurs on the day preceding the bombing, it is more
than likely that the volatile substances would have been contaminated
• Also, similar compounds have similar retention times which can be mistaken
SCANNING ELECTRON MICROSCOPE /ENERGY
DISPERSIVE X-RAY (SEM/EDX)
•
Limitations:
• Was unable to detect sulphur from the explosion
• “Although high explosives are used to initiate and boost low explosives, they are
usually totally consumed in the ensuing reaction and rarely leave traces for the
forensic chemist to find...”
ASSUMPTIONS/FLAWS
•
“In order to mount an argument that an inorganic ion was part of the explosive mixture,
the forensic analyst must demonstrate its concentration to be significantly higher in and
around the crater than in the background.”
• “A large number of analyses may be required to achieve this objective.”
• “At this stage of technological development there are no instruments available on the
market for such applications”
•
“Soils from in and around the blast seat were analyzed by scientists from the AFP using
X-ray fluorescence spectroscopy. No evidence was found to indicate higher than
background levels of any of the elements implicated.”
• “Although high explosives are used to initiate and boost low explosives, they are
usually totally consumed in the ensuing reaction and rarely leave traces for the
forensic chemist to find.”
SAMPLING TECHNIQUES
•
Circumstances which may affect samples and therefore test results
•
Amount of sample collected
•
Exposure
• Reaction with environment
• Volatility
•
•
Contamination
•
Time laps before testing of sample occurred
•
Long distance travel of sample
•
Etc.
“The quantity of post blast residual matter was reduced through dissolution and being washed
away down gutters and drains. The warm and humid climate of the tropics compounded the
problem as atmospheric moisture combined with the fuels and carbonaceous materials to
further reduce the amount of reactive chemicals to be found”
DETERMINATION OF BACKGROUND LEVELS
•
Circumstances which may negatively effect the background reading with which samples
are compared to
• If the background reading is taken too far from the blast site it may not have an
accurate depiction of the levels of various substances found in the area
• If the background reading is taken too close to the blast site it may be contaminated
with substances from the blast itself, thereby contaminating the sample and skewing
data
FLAWS IN USING A MOBILE LABORATORY
•
There is a fine line in determining how close to the scene a mobile lab should be as to be
convenient, yet far enough away to minimize the risk of contamination
•
“The rationale behind a mobile laboratory is to produce timely, albeit tentative findings for
the investigators whilst reducing the number and volume of samples to be sent to the
main laboratory for more exhaustive confirmatory analyses”
• These tests are not conclusive and if there are findings it only allows for further
testing
• These test are also not very accurate, which means there may be false positives, but
also false negatives. False positives would most likely be followed up on, but false
negatives may not be as the mobile lab would determine them to be not as important
• If there are already trace amounts of substances and contamination present doing
these tentative tests may limit the amount of material left for more conclusive test to
be ran and may cause further contamination of the sample, thereby hindering rather
than furthering the investigation
CONCLUSION
•
These techniques and methods were not accurate enough to draw the conclusions that
the forensics team had done in this investigation. They were informed of important details
from the suspect that confessed and worked backwards using this information. If they had
not been supplied with this information, more careful techniques would need to be
employed to determine key aspects of the case (such as bomb materials, amounts, etc.)
• A more careful analysis would aid the investigation
• Ex. Bombing materials used, check for recent purchases, etc.
•
These types of careful analysis were not required as the team “got lucky” off of the van
code that was traced back the the suspect which confessed and aided in the discovery of
substances and amounts used in the bombs from which the forensic team then tentatively
confirmed