Smart Facts – Forensic science and separating techniques

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  1. Forensic scientists analyse evidence to help solve crimes. They often use separation techniques.
  2. Chromatography is used to separate substances in a mixture. They are different types including paper, TLC (thin layer chromatography) and gas.
  3. In chromatography the plate or paper used is called the stationary phase. The solvent that travels up it is called the mobile phase. The solvent used has to dissolve the mixture that you want to separate.
  4. Paper chromatography is used to separate out the pigments in ink or paint, for example to find the pen that wrote a document. It works because some pigments are more soluble than others – these travel further up the paper than the less soluble ones.
  5. Gas chromatography can be used by forensic scientists to test how pure a substance is. Pure substances only contain one type of element or compound. The opposite of a pure substance is a mixture.
  6. Pure substances have specific melting and boiling points. If there are contaminants present these temperatures will change.
  7. Distillation is used to separate a mixture of substances with different boiling points, such as ethanol and water. The ethanol will boil first and turn into a gas. If you cool the gas it will condense into pure ethanol.
  8. Forensic scientists may use filtration to separate a soluble substance from an insoluble one. For example, if they want to test the pH of a soil sample they add water to dissolve the minerals in the soil and then filter the mixture. They will test the liquid (filtrate) with a pH probe.
  9. In DNA fingerprinting fragments of DNA are separated to form a pattern unique to an individual.
  10. Forensic scientists carry out DNA fingerprinting on tissues samples, like blood and hair, found at a crime scene. They can use this to identify a person.