Lecture 6 - Explosions 6

Question 1

what are the three types of scientific evidence used in explosive investigation

Answer 1

classification - are explosives linked
identification - what is it
quantification - how much is there

Question 2

what are the three S’s used in explosive investigation

Answer 2

Selectivity - determine the analyte from a mixture

Specificity - only the analyte contributing to the end result

Sensitivity - the calibration curve - limit of detection and limit of quantification

Question 3

what can the selectivity in explosive investigation be affected by

Answer 3

contamination of samples from the lab or surrounding environment

Question 4

When is the evidence you present likely to be question (associated with the amount of it that you have)

Answer 4

if the amount if close to the LOD or LOQ of the instrument you are using

Question 5

what may co-elution in the chromatogram mean

Answer 5

we can’t be 100% sure the peak seen is from the analyte and not another source

to do with the specificity of the method

Question 6

what are the two main purposes if an explosive investigation

Answer 6

the initial investigation = what happened - think what evidence may be needed

presenting evidence at trial - what can you prove happened

Question 7

what are some locations explosive residue may be detected (5)

Answer 7

• a suspect’s hands, clothing, body, face, hair
• scenes where an explosion have occurred
• Clandestine labs or explosive storage dumps
• consider how an explosive may have been stored/transported
• consider household/accessible items that may have been used to make an explosive

Question 8

what is the first priority when attending a scene with an expected explosion/explosive

Answer 8

safety of everyone - the explosive and surrounding area needs to be deemed safe before investigation proceeds

Question 9

if the material at the scene have been encountered before what three things could be estimated

Answer 9

the explosive power of the explosive

the materials that have been used

if the explosive could be a viable explosive

Question 10

if the material used to create the explosive have not been seen before why do we need to be more careful when dealing with it

Answer 10

we would be unaware of the chemistry and potential damage it can cause

how sensitive it is

so can be a danger

Question 11

what are 4 questions as the investigator you should ask yourself when dealing with an explosive scene

Answer 11

was it a solid or liquid?

what was it?

how was it used?

how was it initiated?

Question 12

what may suggest a liquid explosive has been used

Answer 12

scattered droplets around the point where the explosive was

Question 13

what can indicate the type of detonator used to set off an explosive

Answer 13

strands and fuses that may have been left behind

can estimate if there was a blasting cap and what this was made of

Question 15

how is the point of detonation often recognised

Answer 15

by a crater - especially on soft ground

but if none are seen the explosive is likely to not have been set off on the ground

Question 16

are residues more likely or unlikely to be easily found at an explosive scene

therefore what is it important to do when arriving at the scene

Answer 16

unlikely as the explosion causes material to be blown away from the point of detonation- evidence is likely to be scattered a considerable distance

make sure to cordon is set to an appropriate distance

Question 17

what do all personnel entering the scene need to wear

Answer 17

PPE - gloves, shoe covers, overalls, gloves

to protect the scene

Question 18

what type of evidence should be collected from explosive scene

Answer 18

collect all loose soil and debris package in sealed labelled containers

things that may indicate the type of detonation = blasting cap, electronic timer, phones

things that might indicate the storage/container of the explosive = pipes, plastic tubs (melted or deformed)

Question 19

give two places residues are likely to be found

Answer 19

embedded in nearby soft objects such as wood, rubber or bodies

on the surface of nearby metal objects e.g cars, road signs

remember crime scenes are 3D

Question 20

what affects the distance residue is scattered from an explosion

Answer 20

the amount of gas produced

Question 21

do high or low explosives generally leave more residues at the scene

Answer 21

low explosives - not as powerful

Question 22

what can be useful for scene investigators with the use of impr0vised explosive devices

Answer 22

they often don’t fully explode or the detonator malfunctions so can be easily identified

Question 23

name two analytical methods that can be used for rapid screening of bulk residues at explosive crime scenes

Answer 23

portable instruments such as suitcase GC or handheld Raman

for the identification of materials used in the explosive material

Question 24

name three types of spectroscopy used in the lab for analytical analysis of explosive evidence

Answer 24

IR spectroscopy
raman spectroscopy
X-Ray - SEM-EDX

Question 25

name four types of separation techniques used in the lab for analytical analysis of explosive evidence

Answer 25

HPLC
GC
Ion chromatography
Electrophoresis

Question 26

name four types of detector used in the lab for analytical analysis of explosive evidence

Answer 26

mass spectrometer
UV/Vis
Flame ionisation
Ion Mobility

Question 27

what are the benefits of using IR or raman spectrometers for analysis here (3)

Answer 27

quick
non destructive
give characteristic bands of particular elements/bonds

Question 28

how is SEM used here

Answer 28

to look at the physical characteristics of particulates in detail

considering size and arrangement

Question 29

how is EDX useful here but what is the disadvantage of this method

Answer 29

elemental identification of the metallic components - scan across fragments and see if the element if above normal levels

time consuming

Question 30

what is GC particularly good for identifying

Answer 30

volatile compounds

Question 31

what is ion chromatography good for separating here

Answer 31

charged organic compound e.g nitrates and chlorates

Question 32

what is electrophoresis good for separating

Answer 32

ionic and charged compounds due to the electrodes having +ve and -ve charges

Question 33

when are UV-Vis detectors normally used

Answer 33

with HPLC

Question 34

when is using mass spectrometry as the detector method good

Answer 34

for trace analysis as it is very sensitive

Question 35

what is the name of the technique needed for analysis of trace explosives

Answer 35

clean room techniques

Question 36

what in clean rooms needs to be tightly controlled and why

Answer 36

the background levels of explosive materials

to prevent sample contamination to ensure the evidence presented is robust so is admissible in court

Question 37

name 4 control measures used in clean rooms

Answer 37

positive air pressure - pressure is higher inside the lab than out so air diffuses out not in

HEPA (high efficiency particulate air) filters - remove particulates that contaminate

monitor of air particulates - regularly checking background levels as analysts can bring things into lab from outside

use of disposable equipment - gloves, shoe covers, lab coats - these are double bagged on entry and exit

Question 38

what features do clean rooms have to control contamination even further (2)

Answer 38

separate examination and instrument benches

a separate kit room to get changed

Question 39

when environment samples of the clean room are taken, what action is done if the explosive residue in the background is below 5ng

Answer 39

no action

Question 40

when environment samples of the clean room are taken, what action is done if the explosive residue in the background is between 5 and 10 ng

Answer 40

confirm the identity of the explosive and clean the area

Question 41

when environment samples of the clean room are taken, what action is done if the explosive residue in the background is between 10 and 100ng

Answer 41

clean the area and re-test until the sample tests negative

pause all other analyses until the levels drop down

Question 42

when environment samples of the clean room are taken, what action is done if the explosive residue in the background is above 100ng

Answer 42

identify the contamination source, look at casework that may have been affected and repeat it, clean and re-test until sample is negative

Question 43

where is contamination entering the lab likely to come from (2)

Answer 43

from the analyst

from the evidence collected by the police force - they can’t always and don’t always do this in a controlled way

Question 44

what is the difference between trace and bulk analysis of explosive evidence

Answer 44

bulk = mg or more
- quantitative analysis
- paired with non chemical evidence
- can be done on site

trace = 10 to 100ng
- tends to be challenged in court
- needs to use of clean rooms
- often has higher uncertainties

Question 45

name three types of sampling methods used to process trace and briefly explain them

Answer 45

static headspace sampling:
- sample heated in a sealed container
- headspace injection into GC

dynamic headspace sampling:
- inert gas is pushed into the sample vial
- the headspace is drawn into a solid phase trap which retains explosive vapours
- sample is concentrated before it injected into GC

SPME (solid phase microextraction):
- preconcentrate sample before injection
- fused silica fibre coated with stationary phase (e.g PDMS) injected into tube
- sample adheres to the fibre and desorbs by heating from stationary phase into the GC injector

Question 46

what type of sampling is best for trace analysis

Answer 46

dynamic headspace sample as the sample is concentrated before it is injected into the GC

Question 47

how is SPME a dual function process

Answer 47

recovers trace samples and pre-concentrated the sample before injection

Question 48

what is extracted from the headspace of vials in the sampling process

Answer 48

the volatile components

Question 49

name three ways explosive particulates can be recovered

Answer 49

swabbing
- good for smooth surfaces

vacuuming
- good for fabrics
- little vacuums with filters

solvent wash
- sonicate whole sample in extraction solvent

sonicate = agitate samples to get more out of it

Question 50

what types of solvents are used when swabbing explosive residues

Answer 50

polar mixtures

e.g water/acetone
water/MeOH

Question 51

how are samples cleaned/pre-concentrated in sampling explosives

Answer 51

SPE - solid phase extraction

• the use of a small cartridge containing a sorbent material to adhere the sample to

Question 52

what are the 4 types of SPE used when pre concentrating and cleaning explosive samples

Answer 52

normal phase = absorbs polar compounds (has polar groupd e.g OH)

reverse phase = absorbs non polar compounds (has hydrocarbon chains)

ion exchange = good for inorganic components

size exclusion = absorbs lower molecular weight molecules

can do a combination of these e.g reverse phase followed by size exclusion

Question 53

what type of SPE technique would be suitable for separating picric acid and TNT

Answer 53

reversed phase - this will adsorb picric acid and allow TNT to elute through

Question 54

explain the process of SPE conditioning for the analysis of an inorganic species

Answer 54

clean the sorbent e.g with ethyl acetate

condition the sorbent e.g with ethano/water mix

apply the sample

wash the sorbent e.g with ethanol/water then MTBE/pentane

elute the explosive/analyte using ethyl acetate

inorganic components wash through with polar or non polar solutions

Question 55

what are the two main steps involved in explosive analysis

Answer 55

a separation followed by a detection system

Question 56

name two explosive specific detection systems and what they are specific for

Answer 56

chemiluminescence = specific detection of C-NO2, N-NO2 and O-NO2 groups

thermal energy analysers = controlled pyrolysis to form NO

Question 57

why are the standard analytical techniques GC-MS LC-MS not always good at providing sufficient evidence in explosive analysis

Answer 57

many non explosive compounds may have very similar molecular weights or retention times to explosive ones so can get confused