Chemical techniques

1. Chemical techniques Booklet to help with unit 32 P2

2. Mass Spectrometry This can be used to determine what is in an unknown sample. Examples of it’s applications: • To deduce if a drink been spiked with a drug • To detect illegal dumping of poisons into a local river • To detect and identify the use of steroids in athletes

3. Mass Spectrometry The main stages of mass spectrometry include: • Ionisation of substances to change the molecules into charged particles, followed by acceleration and deflection of the charged particles followed by detection of the molecular weight of the charged particles. • The molecular weight can be used to deduce what thee identity of the substances are

4. Infra-red spectroscopy This is used to assess purity and identify what functional groups a molecule contains. Example of its applications • Analysing layers of paint in chips from the clothes of a victim involved in a hit and run accident (the specific make, model, and year of the vehicle can be identified)

5. Infra-red spectroscopy It involves using infra-red (IR) which is a type of electromagnetic radiation which is absorbed by the bonds in organic substances. Different types of organic functional groups will absorb different wavelengths of the IR radiation. We can use IR spectroscopy to determine what wavelengths have been absorbed by a chemical that we are analysing and then look up in a chemical data book what the functional groups of that specific wavelength are.

6. Ultra Violet spectroscopy This is used to assess purity and helps to identify unknown substances in forensics. Example of its applications • The concentration of poison found in a contaminated beverage. • To check that chemicals in drinking water does not exceed the legal limit.

7. Ultra-Violet spectroscopy It involves using ultraviolet (UV) which is a type of electromagnetic radiation which is absorbed by inorganic substances. Different amounts/concentrations of inorganic substances will absorb different amounts of UV radiation. We can use UV spectroscopy to determine the concentration of a chemical substance in forensics

8. Colorimetry spectroscopy This is used to assess purity and helps to identify unknown coloured substances in forensics. Example of its applications • The concentration illegal coloured substances dumped into a local river.

9. Colorimetry spectroscopy It involves using light rays which is a type of electromagnetic radiation which is absorbed by coloured substances. Different amounts/concentrations of coloured substances will absorb different amounts of light radiation. We can use colorimetry to determine the concentration of a coloured chemical substance in forensics

10. Paper chromatography This is used to determine the identify of unknown components in mixtures For example: • If a food dye contains a banned chemical

11. Paper chromatography • It requires a solvent to separate the components used to make up a mixture (e.g. food dye) on a paper. It will then be used to determine what the components are measuring their Rf values and looking these up in a chemical data book

12. Thin layer chromatography This is used to determine the identify of unknown components in mixtures For example: • If a drug contains any illegal substances

13. Thin layer chromatography • It requires a solvent to separate the components used to make up a mixture (e.g. food dye) on a thin layer plate usually made up of silca. It will then be used to determine what the components are measuring their Rf values and looking these up in a chemical data book

14. Gas liquid chromatography • This is when an inert gas is used to separate the components of a mixture • It is often used to analyse urine samples of athletes to determine if their urine (which is a mixture) contains a banned substance

15. Gas liquid chromatography • An inert gas like hydrogen gas carries the mixture in an oven which is made up of thin layered columns. Some components will be carried faster than other components. • The speed that the components are carried by the inert gas in the oven can be looked up in a chemical data book.

16. High performance liquid This is also known as “High pressure liquid” chromatography. Examples of this being used is: • To test water samples to look for pollution in lakes and rivers • To analyse metal ions and organic compounds in solutions (include content of blood found at crime scenes).

17. High performance liquid • A column composed of silica or alumina gel powder or suspension beads in a liquid is set up. • A solvent is forced down a long column using pressure. This solvent will then be used to push a mixture of unknown chemicals down the column. • Some components will be travel down the column faster than other components.

18. Toxicology • This is the scientific study of poisons and drugs of abuse. • Forensics will analyse urine, blood and other biological tissues to determine what poisons or drugs it may contain • Examples of the different techniques used in toxicology are in the next few slides

21. Chemical presumptive tests • These are used in violent crimes or where bodily fluids such as blood may be prevalent • Blood can be tested using the reagent called Luminol which is sprayed over a surface which will react with haemoglobin in red blood cells and change into a dark blue colour. Luminol is very sensitive and detects minute traces of blood.

22. Chemical presumptive tests • Semen can be detected using AP reagent. The reagent is actually an enzyme that catalyses the conversion of sodium-napthylphosphate (which is found in semen) into napthyl which changes into a purple colour. • Saliva can be detected using the Phadebas reagent. It detects the presence of amylase which is an enzyme found in saliva.

23. Enhancing fingerprints • This involves using chemicals to show up fingerprints left behind in a crime scene. • Ninhydrin is used to show up latent prints on porous items. It reacts with the amino acid that can be found in sweat which is left behind by fingerprints. It reacts with amino acids and changes into a blue coloured substance.

24. Enhancing fingerprints • Iodine fuming is one of the oldest techniques used to develop latent fingerprints but is not now commonly used in the forensic laboratory. This works best with fresh prints that are no more than a few days old, and can be used in both porous and non-porous surfaces. It reacts with amino acids from sweat left behind in a fingerprint to form a black colour (which will show up the fingerprint).