Embedded Files
Today we are learning about chromatography
Today we are learning about chromatography
So that we can understand how chromatography is used in arson investigation
So that we can understand how chromatography is used in arson investigation
We will be able to complete the chromatography prac
We will be able to complete the chromatography prac
How is Chromatography used in Arson investigations?
How is Chromatography used in Arson investigations?
Chromatography is a technique used to separate mixtures. Information from a chromatography investigation can also be used to identify different substances.
Even in a large fire, accelerant residues of flammable liquids may be left behind.
Common: gasoline, kerosene, fuel oil
Less common: alcohol, paint thinner, Unusual burn pattern may suggest use of liquid accelerant.
Collection of Evidence
Accelerant remains can be detected by tracing the point of origin or canine use.
Object containing accelerant must be packaged in air tight container.
Storage of Evidence
Metal cans: airtight, but old cans may rust
Glass Jars: rubber or glued liners may interfere with results.
Special airtight plastic evidence bags: must be properly sealed
Passive Headspace Sampling
In passive headspace sampling the container is heated to volatilize any ignitable liquids remaining in the sample.
Activated charcoal is suspended in the headspace to absorb the volatilized liquid.
The charcoal is then removed from the sample container and the liquid is removed from it by solvent extraction.
Analysis of Accelerants
Gas Chromatography separates components and Mass
Spectrometry identifies the components.
Chromatography Prac
Chromatography Prac
In chromatography the mixture is passed through another substance, in this case filter paper. The different colour ink particles travel at different speeds through the filter paper allowing you to see the constituent colours of the pen ink.
All types of chromatography have two phases. A mobile phase where the molecules can move and a stationary phase where the molecules can’t move. In the case of paper chromatography the stationary phase is the filer paper and the mobile phase is the solvent ( water ).
The more soluble the ink molecules the further they are carried up the paper.
This video shows chromatography in action.
WHY DOES CHROMATOGRAPHY WORK?
When the filter paper containing the ink spots is placed in the solvent ( in this case water ) the dyes travel through the paper.
Different dyes in ink travel through the chromatography filter paper at different speeds. The most soluble colours dissolve and travel further and faster than less soluble dyes which stick to the paper more.
YOU WILL NEED:
Filter paper or paper towel
Felt tip pens – not washable or permenent
A container – glass, jar or plate
A pencil
INTRUCTIONS:
Pour a small amount of water onto a plate or into the bottom of a jar.
Find a way to suspend the filter paper over the water so just the very bottom is touching the water. If you do the experiment in a jar the easiest way to do this is to wrap the top of the filter paper around a pencil, clip it in place and suspend it over the top of the jar.
Our LEGO holder worked well too!
Use the felt tip pens to draw a small circle about 1cm from the bottom of the filter paper with each colour pen you want to test.
Suspend the filter paper in the water and watch as the ink moves up the filter paper.
You should end up with something like this! We call the finished filter paper, a chromatogram.
Be sure to collect and upload evidence of your work to Compass!
(photos etc)
WHAT HAPPENS IF YOU USE WASHABLE PENS?
If the colours are washable they tend to just contain one type of ink and so you don’t see any separation of colour.
You can see below that only a couple of the inks have separated out, compared to the non washable pens above.
WHY DOES CHROMATOGRAPHY WORK?
When the filter paper containing the ink spots is placed in the solvent ( in this case water ) the dyes travel through the paper.
Different dyes in ink travel through the chromatography filter paper at different speeds. The most soluble colours dissolve and travel further and faster than less soluble dyes which stick to the paper more.
This practical was taken from science-sparks.com, and was created by Emma Vanstone
Research other areas in which chromatography is utilized within forenzics (eg, DNA analysis) and provide an explanation on how this works. Put your research into the google form below.
Research other areas in which chromatography is utilized within forenzics (eg, DNA analysis) and provide an explanation on how this works. Put your research into the google form below.
Page updated
Report abuse