Lecture 21 - gemstones, metals, GSR, fireworks Flashcards
what are three properties used in the analysis of gemstones
fluorescence = when exposed to short or long wave UV they emit visible light
phosphorescence = if luminescence continues after exposure to UV due to impurities and defects in the crystal lattice
birefringence
what are the two techniques used to characterise the chemical and physical properties of gemstones
Surface microscopy
- SEM
- TEM
- atomic force
Bulk Diffraction
- X-Ray (XRD)
what is the law used to understand the conditions required for diffraction
Bragg’s law = a equation that relates the wavelength of X-rays to the angle of reflection from a crystal.
what is XRD used for
the establish the arrangement of atoms within a crystal structure and how they stack together
what can XRD be used to identify in gemstones (3)
impurities and defects in the crystal lattice
metal inclusions to the crystal e.g copper
addition of glass given by broad peaks
what two things that can be measured of gemstones allow us to identify it and compare it to a known sample
the retardation and birefringence
what are sources of metals that can be used in trace evidence (5)
rust or metal shavings from substances e.g pipes or weapons such as a crowbar
GSR = gunshot residue
explosive residue
fireworks and sparklers
lightbulb filaments
what analytical technic can be useful in gemstone analysis
Raman
as this can identify inorganic components
what are two tests regularly used pre analysis of GSR
colour spot
presumptive chemical tests
name 6 of the primary techniques used in the analysis of metals as trace evidence
SEM-EDX
XRD
XRF
HPLC and GC-MS
AAS
LA-ICP-MS
what are the two types of GSR found in firearm related events where do each of these come from
inorganic GSR
- from primer mixture and some of the cartridge case
- tends to have heavy metal components
organic GSR
- from smokeless powder, explosive component, stabilisers, plasticisers, sensitizers and flash inhibtors
what happens in the optical methods category in GSR detection
identification of organic compounds
using strong IR luminescence properties
non destructive and fast
low specificity and high LoD
where are combustion products found on firearms (2 locations)
spent cartridges and muzzle of the firearm
what are the 4 categories within GSR detection
- optical methods
- chemographic testing
- spectrometry
- separation method
what happens in the chemographic testing category in GSR detection
can be done on scene
presumptive test looking at inorganic compounds
high selective but only qualitative with risk of false positives
what happens in the spectrometry category in GSR detection
identify inorganic components
SEM-EDX is most commonly used as quantitative, highest compositional and morphology detail but time consuming
what happens in the separation category in GSR detection
coupled with mass spec to look at components
LC or GC MS
destructive
reliable, specific and low LoD
how can metals be detected in latent fingermarks
using X-Ray fluorescence microscopy
can link the presence of metal objects to handling of gun barrels or ammunition cartridges
what method is commonly used in explosive trace detection
ion mobility spectrometry (IMS)
separates and identifies ionised molecules present in the gas phase based on their mobility in a carrier buffer gas
where is IMS particularly a good method and why
in a situation where fast and reliable results are needed e,g airports
measurements can be done in milliseconds
what other techniques are useful in analysing the organic and inorganic components of explosive evidence (5)
GC
LC
SEM
FTIR
Raman
what 4 trace evidence types are fireworks a combination of
paper
plastic
explosives
metals
what are sparklers used for
to initiate homemade explosives
techniques can’t determine between brands of sparklers yet
what technique is used to analyse the presence of sparklers
use ICP-MS to detect the elemental profile of 7 metal components and then use chemometrics
