Download CASE STUDY 1

CASE STUDY 1
The Bali bombings
Overview
• In 2002, the Bali bombings killed 202 people from 22
countries
• “Operation Alliance” involved Australian Federal Police
(AFP), Indonesian National Police (INP), Victoria Police
Forensic Services Centre (VPFSC), Britain Forensic
Explosives Laboratory (FEL), etc.
• 3 explosions: a bar, a night club, a street outside
American and Australian consulate buildings
• Forensic chemists used a “mobile laboratory” to
recover residues from blast scenes and suspect’s
residences to determine bomb compositions
THE EVIDENCE
Bomb 1
-tiny fragments of tartan fabric were recovered from site
surrounding the blast epicentre
-connective tissue and spatter marks were visible on the
ceiling above the epicentre
-absence of a crater
Bomb 2
-inspection number found on chassis rail of car was traced
back to owner
Explosions
• result from a rapid release of gas
• two main types of explosives: low velocity and high
velocity
1. Low velocity explosives, like ammonium nitrate, used
mainly in mining and for “pushing” applications
2. High velocity explosives, like pentaerythritol tetranitrate
(PETN) and TNT, used in detonators, military etc. Usually
used to initiate/boost low velocity explosives. Usually
consumed and rarely leave traces
• most large bombs consist of some form or combination of
nitrate, chlorates, perchlorates, diesel oil, sugar, sulphur
and/or aluminum dust
• release of this amount of energy often causes fires
Chemical Structures
• PETN
• TNT
Sample Collection
• Blast scenes are complex due to the spread of
microscopic fragments that can contaminate
evidence
• the concentration of the inorganic ion must be
significantly higher in and around the crater than
in the background
• the main blast produced a fire which was fought
with water, compromising much of the blast
scene
• “mobile laboratory” was used to gather evidence
in a timely matter
Mobile Laboratory
• Nearby motel room was cleared and equipped
with a microscope and camera, an ion
mobility spectrometer (IMS), a portable infrared spectrometer (FT-IR), reagents for
presumptive tests
• Produces rapid tentative results
• Samples must still be sent to main lab for
exhaustive analysis
Sample Testing
• Chlorate ion was detected in 6/2000 samples analyzed
which was considered significant because the highly
reactive nature of chlorate ions make it difficult to persist in
the environment
• Sites it was detected on include the crevices of the blast
crater, and on lamp posts facing the blast
• It was argued that the chlorate ions originated from
unburnt matches falling during the blast so samples were
taken from elevated surfaces
• Scientists from FEL searched the pitting of aluminum street
signs that had been blasted to nearby rooftops using an
SEM EDX. They reported elevated levels of chloride, low
levels of chlorate, and no sulphur was detected.
Presence of TNT at two of the sites was detected
by IMS and confirmed by both GC–TEA and GC–
nciMS
Principles of Chromatography
• A small volume of analyte (1 -10 uL) is taken
up by a needle and injected into a column.
• In GC, the column is a long capillary (20 – 100
m in length) filled with either a liquid or
polymeric solid.
• The injected analyte is moved through the
column by a gas mobile phase (usually Ar, He
or N2) inside the column.
• The different chemical components of the
samples are then separated out according to
the affinity of a given chemical species for the
stationary phase; the retention time for a
chemical species is highly characteristic of that
species.
• GC run times tend to be long relative to LC (as
much as 90 minutes), but the technique is
generally more sensitive than HPLC.
• Liquid chromatography works much the same
way as GC; LC employs short (50 – 300 mm)
columns with a larger bore (2 – 3 mm) packed
with silica beads (2 - 5 um in diameter).
• The surface of the silica can be either silanol
groups (S-OH) or derivaterized with a wide
variety of functional groups. Of particular note
in metabolite analysis are C18 columns.
• The mobile phase consists of a gradient of two
solvents; the solvents used depend on both
analytes of interest and the stationary phase,
but normally include water and an organic
solvent (methanol, acetonitrile, etc).
• Run times on LC systems range from 3 – 60
minutes.
• LC systems are generally able to analyze a
much wider range of compounds than GC, but
can also be less sensitive and less selective.
Principles of Mass Spectrometry
• Once a compound has been ionized upon elution from
a chromatograph, it is pulled into a MS by a vacuum.
The ions go through a series of focusing stages (due to
ever increasing potential differences as it moves
through the instrument) until they reach either a
selector or a detector.
• There are two main types of MS. Single stage MS
measures the mass of parent ions (or daughter ions
from hard ionization sources) without any additional
fragmentation. Useful for detecting and quantifying
parent ions, but does not discriminate between
isomers.
• The most common single stage MS systems
are single-quadrupole and Time-of-Flight
analyzers.
• Tandem mass spectrometry (MS2) can be used
to differentiate between different isomers of a
compound.
• Normally, a quadrupole is used to select for
parent ions of interest, then a second
quadrupole will be used to fragment the ions
by applying a mass-specific radio frequency in
combination with a charged collision gas. A
third analyzer (normally a quadrupole or flight
tube) then selects for one, several or all of the
ions produced.
• Determination of the presence of a chemical
species is highly accurate with MS2.
Colourimetric Testing
• In forensic chemical analysis, colourimetric testing is
used as a qualifier for classes of chemical compounds.
• If the presence of a class of chemical compounds can
be determined, it allows investigators to select an
appropriate analysis method.
• This type of preliminary screening allows for faster
processing of samples, which helps speed up the
investigation, and prevents technicians from running
hundreds or thousands of samples through testing
methods that do not provide useful information.
Colourimetric Methods For
Explosives Screening
Analytical Methods for Explosive Residue
Analysis – Thin Layer Chromatography
• A small amount of an unknown can be
placed on a silica plate (or other
adsorbent material), the bottom of the
plate placed in a mobile phase, and
the retention factors compared to known
standards.
• Used for organic molecule analysis.
• Reasonable detection limit.
• Simple, inexpensive and quick to perform.
• Does not resolve compounds well, but is a good starting point for
analysis, similar to the colourimetric tests described earlier.
• Requires compounds to be visible, either by visible light emission or
by ultraviolet light absorptivity.
• May also be used for MALDI mass spectrometry, although this
precludes any use in quantification.
Gas Chromatography – Electron
Capture Detector
• Volatile compounds are separated out by gas
chromatography, and a chromatogram generated by an
electron capture detector.
• ECDs work by passing gas-phase atoms (the eluent from gas
chromatograph) through an electric field.
• The electric field is generated by a nickel source that ionizes
some of the carrier gas; collisions with the ionized carrier
gas (Ar, N2) will dampen the electric field, which is
measured as a change in the potential across the detector.
• Generally used for halogenated and nitrogen containing
compounds
• Very low detection limits (pg range).
• To facilitate GC, analytes must be volatile and thermally
stable.
High Performance Liquid Chromatography
– Ultraviolet/Diode Array Detectors
• The eluent from an HPLC system is passed
through a UV or DA detector.
• The detectors usually monitor specific
wavelengths; molecules that are known to absorb
and emit at particular wavelengths can then be
detected and quantified.
• Matrix interferences are rarely a problem, but the
method is not particularly selective.
• Highly sensitive technique (can quantify
compounds will into the ng level).
Infrared Spectroscopy
• Infrared emission and absorption is used to generate a
spectrum indicative of the functional groups present in
a sample.
• Useful for structural determination and pattern
profiling (i.e. the spectra produced can be run against
fingerprint databases to rapidly identify samples).
• Useful for both organic and inorganic molecules.
• Very quick to run; low cost in sample analysis.
• Poor selectivity; samples are difficult to clean up and
separate prior to analysis, and so are susceptible to
contamination.
Gas Chromatography – Mass Spectrometry
• Eluent from a gas chromatograph is passed through one of several
different ionization sources, each one leading to different spectra.
• Chemical ionization (CI) generally leads to the production of many
parent ions, with few daughter ions produced.
• Electron ionization (EI) results in heavy fragmentation of analytes;
useful for structural determination, but parent ions do not always
appear in the spectra generated.
• Extremely sensitive technique (perhaps the most sensitive currently
available).
• Samples must be volatile (and stable at high temperature), or easily
and efficiently derivatized to make them so (e.g. methyl
esterification of amino acids).
• Useful for organic materials, lipids, oils and many plasticizers and
stabilizers.
Liquid Chromatography – Mass Spectrometry
• Eluent from a liquid chromatograph (HPLC/UPLC) is
ionized (either through electrospray ionization (ESI) or
matrix-assisted laser desorption ionization (MALDI)).
• Ionized sample is taken into the mass spectrometer
and analyzed by either single-stage or tandem mass
spectrometry (triple quad, QTOF, etc).
• Shorter run times than GC, but less specific (based on
retention times).
• Analytes must be amenable to both LC and ionization
methods available.
• Wider range of analytes can be run than of GC systems.
Scanning Electron Microscopy/ Energy
Dispersive X-Ray Spectroscropy
• Used for surface analysis of very small particle
sizes.
• Used by investigators to examine fragments from
explosions to help determine the source of an
explosion.
• Usable for all physical samples.
• Expensive and time consuming (considering the
large numbers of samples that require analysis).
• Highly skilled operators are required to perform
this analysis effectively.
Example
• If a test with 3% KOH in ethanol determines the
presence of one of TNT, 2,4-DNT and 2,6-DNT,
some of that sample can be sent for further
analysis by LC/MS/MS.
• None of these compounds are volatile, so LC is an
appropriate choice for analysis, while tandem
mass spectrometry can be used to definitively
identify a compound based on structural
elucidation using fragmentation daughter ions.
MS2 of TNT
(taken from http://www.chem.agilent.com/Library/applications/lcms18.pdf)
Types of Bombs
• Bomb 1 – 1-5 Kg of TNT packed into 5 lengths of PVC
pipe sewn into a vest, set off by a suicide bomber
• Bomb 2 – approx. 1 tonne of explosive packed into 12
filing cabinets in a van, cabinets connected via
detonating chord made from PETN, explosives a
mixture of potassium chlorate, sulphur and aluminum
boosted with TNT, the power was equivalent to 150 Kg
TNT, set off by a suicide bomber
• Bomb 3 – small amount of TNT set off by a mobile
phone