Forensic Science - Analytical Techniques

What 3 methods can be used to lift footprints?

• Casting

• ESLA

• Gelatine lifts.

What does ESLA stand for?

Electrostatic lifting apparatus.

What kind of footprints is ESLA the best for?

Latent prints.

How does ESLA work?

Static electricity lifts dust particles from the surface the print is on.

It creates a replica of the print.

This can then be photographed.

What kind of footprint are gelatine lifts the best for?

Latent.

How do gelatine lifts work?

The gelatine lifter is placed over the latent print.

It is smoothed down to ensure good contact with print.

The dust clings to the gel.

Gel is peeled off carefully, leaving a print ready to be photographed.

What method should be used to analyse a suspect tool mark, and a control mark?

A comparison microscope.

What does ACE-V stand for?

• Analysis.

• Comparison.

• Evaluation.

• Verification.

What happens at the analysis stage?

Assessment of the crime scene mark.

What happens at the comparison stage?

A side-by-side comparison of two marks, trying to determine whether they’re a match or not.

What happens at the evaluation stage?

A conclusion is drawn whether they’re a match.

What happens at the verification stage?

Another examination is taken place by a different examiner, to see if they reach the same conclusion.

Name a method to reduce a sample.

Cone and quartering.

Name 3 methods to remove the analyte from the matrix.

• Headspace extraction.

• Liquid-liquid extraction (LLE).

• Solid phase extraction (SPE).

How does headspace extraction work?

• Sample is placed in a sealed container and heated up.

• Analyte moves into the headspace above the sample.

• The analyte is separate, and can be extracted using a syringe and then analysed using other methods.

How does liquid-liquid extraction work?

• The sample and another liquid that repel each other are mixed together.

• The analyte will move into the liquid it is more soluble in.

• The liquids separate and the layer with the analyte is collected.

How does solid phase extraction work?

• The liquid sample is passed through the solid phase.

• The analyte sticks to the solid, the rest of the liquid washes through.

• This separates the analyte from the matrix.

What are the 3 methods of analysing ink?

• FTIR.

• MSP.

• TLC.

How does FTIR work for analysing ink?

• Infrared light is shined on the ink.

• Each chemical bond absorbs light at different frequencies.

• Each type of ink has a different chemical ‘fingerprint’.

FTIR tells ink apart by reading how their molecules absorb infrared light.

How does MSP work for analysing ink?

MSP distinguishes inks by measuring and comparing how they absorb visible light (their color signature).

How does TLC work for analysing ink?

TLC separates ink into its individual dyes so inks can be compared by their spot patterns.

Name a spot test that can be carried out on GSR.

The Griess test (nitroglycerine).

What colour change occurs when nitrites are present in the Griess test?

Orange / red.

What is the main method used to examine GSR?

SEM-EDX.

How does SEM-EDX work?

• Scanning electron microscopy (microscope with focused beam of electrons.

• Combined with energy dispersive x-ray.

• Allows us to see the GSR, as well as seeing its elemental composition.

What colorimetric test can be used to examine explosives?

The Griess test (orange/red colour change).

Presumptive.

Name 2 methods of analysis for explosives.

• GC-MS (separates chemicals by heat, able to identify their makeup due to different heating points).

• SEM (allows for examination of particles as they are very magnified and detailed).

Name 2 methods for analysing accelerants.

• Headspace extraction first (prepare for next step).

• GC-MS.

Name a screening test used to test for cocaine.

Cobalt thiocyanate.

Name a method for confirming the presence of drugs.

• GC-MS (separates the different components).

What is the first step in blood analysis?

Centrifugation.

Name 3 saliva tests.

• Phadebas.

• Starch-iodine.

• Radial diffusion.

Name 2 confirmatory ways to test for semen.

• Microscope.

• Prostaglandin test (detects prostate specific antigens).

How do you test a stain for urea?

• Urease added to stain.

• If urea present, urease reacts and produces ammonia.

• Colour change from yellow to pink.

Name 2 methods of analysing paint.

• Microscope (can see the layers, see if they match).

• FTIR (different paint components absorb different amounts of light, a spectrum is created, allows us to see its chemical makeup).

What does GRIM stand for?

Glass refractive index measurement.

How is GRIM used to analyse glass?

• Measures how light bends through the glass.

• Compares refractive index values between samples.

Name 3 methods of analysing fibres.

• Light microscopy (colour, scale pattern, shape, diameter).

• Comparison microscope (examining 2 samples at same time).

• FTIR (shining infrared light through fibres to see their makeup).

Name 3 methods for analysing soil.

• Munsell colour chart.

• Compound microscope (particle size).

• SEM (mineral composition).

Name 3 presumptive tests for blood.

• Catalytic colour test (relies on haemoglobin).

• Chemiluminescence test (light is emitted from chemical reaction).

• Fluorescence.

Give an example of a chemiluminescence test.

Luminol.

Give 2 examples of catalytic colour tests.

• Kastle-Meyer test (turns pink if blood is present.

• Leuco-Malachite Green (turns green/blue if blood is present).

Name 2 microcrystalline tests for blood.

• Takayama (pink feathery crystals).

• Teichmann (brown rhombic crystals).