Lecture 21 - gemstones, metals, GSR, fireworks

Question 1

what are three properties used in the analysis of gemstones

Answer 1

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

Question 2

what are the two techniques used to characterise the chemical and physical properties of gemstones

Answer 2

Surface microscopy
- SEM
- TEM
- atomic force

Bulk Diffraction
- X-Ray (XRD)

Question 3

what is the law used to understand the conditions required for diffraction

Answer 3

Bragg’s law = a equation that relates the wavelength of X-rays to the angle of reflection from a crystal.

Question 4

what is XRD used for

Answer 4

the establish the arrangement of atoms within a crystal structure and how they stack together

Question 5

what can XRD be used to identify in gemstones (3)

Answer 5

impurities and defects in the crystal lattice

metal inclusions to the crystal e.g copper

addition of glass given by broad peaks

Question 6

what two things that can be measured of gemstones allow us to identify it and compare it to a known sample

Answer 6

the retardation and birefringence

Question 7

what are sources of metals that can be used in trace evidence (5)

Answer 7

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

Question 7

what analytical technic can be useful in gemstone analysis

Answer 7

Raman

as this can identify inorganic components

Question 8

what are two tests regularly used pre analysis of GSR

Answer 8

colour spot
presumptive chemical tests

Question 9

name 6 of the primary techniques used in the analysis of metals as trace evidence

Answer 9

SEM-EDX

XRD

XRF

HPLC and GC-MS

AAS

LA-ICP-MS

Question 10

what are the two types of GSR found in firearm related events where do each of these come from

Answer 10

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

Question 11

what happens in the optical methods category in GSR detection

Answer 11

identification of organic compounds

using strong IR luminescence properties

non destructive and fast
low specificity and high LoD

Question 11

where are combustion products found on firearms (2 locations)

Answer 11

spent cartridges and muzzle of the firearm

Question 12

what are the 4 categories within GSR detection

Answer 12

1. optical methods
2. chemographic testing
3. spectrometry
4. separation method

Question 13

what happens in the chemographic testing category in GSR detection

Answer 13

can be done on scene

presumptive test looking at inorganic compounds

high selective but only qualitative with risk of false positives

Question 14

what happens in the spectrometry category in GSR detection

Answer 14

identify inorganic components

SEM-EDX is most commonly used as quantitative, highest compositional and morphology detail but time consuming

Question 15

what happens in the separation category in GSR detection

Answer 15

coupled with mass spec to look at components
LC or GC MS
destructive
reliable, specific and low LoD

Question 16

how can metals be detected in latent fingermarks

Answer 16

using X-Ray fluorescence microscopy

can link the presence of metal objects to handling of gun barrels or ammunition cartridges

Question 17

what method is commonly used in explosive trace detection

Answer 17

ion mobility spectrometry (IMS)

separates and identifies ionised molecules present in the gas phase based on their mobility in a carrier buffer gas

Question 18

where is IMS particularly a good method and why

Answer 18

in a situation where fast and reliable results are needed e,g airports

measurements can be done in milliseconds

Question 19

what other techniques are useful in analysing the organic and inorganic components of explosive evidence (5)

Answer 19

GC
LC
SEM
FTIR
Raman

Question 19

what 4 trace evidence types are fireworks a combination of

Answer 19

paper
plastic
explosives
metals

Question 20

what are sparklers used for

Answer 20

to initiate homemade explosives

techniques can’t determine between brands of sparklers yet

Question 21

what technique is used to analyse the presence of sparklers

Answer 21

use ICP-MS to detect the elemental profile of 7 metal components and then use chemometrics