32.2 Forensic Chemical Techniques

1. 32.2 Forensic Chemical Techniques Spectrometry, colorimetry, ultraviolet, infrared and mass spectrometry

2. Learning Objectives • Be able to use chemical techniques to analyse evidence from a simulated crime scene

3. Spectroscopy • Different substances absorb light in different frequencies, which causes dark bands to appear in the spectra. • Helium was discovered through spectroscopy - discovered in the Sun before it was found on Earth.

4. Spectrophotometer • Used to analyse EM spectra • Measures absorption of UV, visible or IR

5. Colorimetry • How do we actually see things? We see things because they reflect light into our eyes Homework

6. Colorimetry • Visible light spectrum ranges from 380nm to 750nm • Between UltraViolet and InfraRed • All the colours combine to make white light

7. Colorimetry The colour an object appears depends on the colours of light it reflects. A red object looks red because it absorbs all other colours except for red which it reflects. White light • Blue, green & yellow light (400-650nm) is absorbed. • Red light (650-800nm is reflected.

8. A pair of purple trousers would reflect purple light (red and blue, as purple is made up of red and blue): Purple light A white hat would reflect all seven colours: White light

9. Colorimetry • Measures the wavelength and frequency of the visible light absorbed. If this is unique to substance, this can be used to identify that substance. • Can also determine the concentration of a sample. • The Beer-Lambert Law – “absorbance is directly proportional to the concentration of a solution”

10. Colorimeter Place substance in colorimeter A beam of white light is passed through the substance The atoms of the material absorb light at certain frequencies. The instrument detects which wavelengths have been absorbed and records this.

11. UV Spectroscopy • aka Fluorescence spectroscopy or fluorometry or spectrofluorometry • Similar to visible light spectroscopy but with UV light • The high-energy UV light excite atoms causing them to fluoresce lower energy light.

12. IR Spectroscopy • Similar to visible light and UV spectroscopy but with IR light • Used to get information about a substance’s structure, purity or to identify it. • The IR waves vibrate the covalent bonds in organic materials. Different types of bonds absorb different wavelengths of IR light

13. IR Spectroscopy Different materials have a distinctive IR “fingerprint”. Can be used to analyse: • Paint chips • Synthetic fibres • Drugs

14. Used to analyse the structure and chemical properties of unknown molecules. Can be used to detect: • Toxins and poisons in water supplies • If food or drink have been spiked • Detect steroid use in athletes Mass Spectrometry (MS)

15. Mass spectrometer

16. The Four Steps • Ionisation : the sample is ionised using a high-energy beam of electrons. This forms positively charged ions by removing electrons from the molecules being anaylsed. • Acceleration: the ions are accelerated until they all have the same energy and are focussed into a beam • Deflection:The ions are passed through a strong magnetic field. This separates them according to their mass and charge. • Detection: The ions produce an electric current that a computer system converts into a mass spectrum.

17. Mass spectrum HexaneC6H14MW = 86.18

18. Activity 32.2A – Spectroscopic Techniques You are a chemical forensic scientist. You have been asked to give evidence in court where you need to explain the different spectroscopic techniques (IR, UV, MS and colorimetry) to the jury. In groups, create a colourful, clear and informative presentation that: • Describes the different types of spectroscopic techniques; and, • Describes the types of evidence they can be used to analyse.

19. Chromatography

20. Chromatography and analysis Describe what is meant by chromatography Describe the differences between paper and thin layer chromatography Use the formula to work out Rf values Describe the process of gas chromatography

21. What is chromatography? Analytical technique used to: • Separate and identify chemicals in a mixture • Check chemical purity • Purify small samples of a chemical

22. What is chromatography? Cheap & simple Expensive & complicated Paper chromatography Gas chromatography

23. Paper and thin-layer chromatography (TLC) • TLC uses paper trapped between 2 slides • Quick, cheap, requires small volumes of solvents • Used to extract dyes from fibres and to identify drugs in forensics • Different solvents are used – water, petrol, alcohols… • Stationary phase = paper • Mobile phase = solvent Paper chromatography TLC chromatography

24. Preparing a Sample • Cut a sheet of paper so it hangs free within a beaker • Mark a sample line ~2cm from the bottom • Place your samples on the sheets

25. Starting the Sample • Place the sheet in a container with a solvent • The bottom of the paper should be submerged into the solvent, but not above the samples • Allow your samples to run at least ½ way up the sample space

26. bsapp.com

27. Allow your samples to dry bsapp.com

28. Interpreting chromatograms • Calculate retention factors (Rf) values • Rf value is a ratio of distance a component sample moves to the distance the solvent moves • This number is usually expressed as a decimal

29. Solvent finish 10 cm Calculating Rf Values • 8 cm • 4 cm Rf = 4/10 = 0.4 Rf = 8/10 = 0.8 • Starting point

30. Gas chromatography • Used to separate complex mixtures • Very sensitive so can detect small values • Not only detects which chemicals but how much of each • Used to look at pesticide residue in food

31. Gas chromatography • Stationary phase = thin film of liquid inside the oven • Mobile phase = gas ie helium (carrier gas) • As compounds come out, they are detected and identified using standards

32. Gas chromatogram of cannabis Recorder response

33. FINGERPRINT CHEMICAL ENHANCEMENT

34. Lesson Objectives • To state the different methods for enhancing fingerprints using chemicals • To describe the methodology of the different techniques • To link Health and Safety issues regarding the chemicals to their use

35. Sweaty fingers… • Sweat is mainly water but also contains salts, sugars, amino acids and proteins • When a finger touches the surface, the sweat is deposited as an invisible latent fingerprint. • We can use chemicals that react with sweat to enhance the fingerprints

36. Ninhydrin • Used for fingerprints on porous surfaces. • Reacts with the amino-acids in sweat to produce a bluish-purple-pink print • Applied via spraying, painting or dipping • Can take hours to weeks to complete the reaction but can be sped up in an incubator

37. Iodine Fuming • The oldest fingerprinting technique • Only works on fresh prints • Used on porous and non-porous surfaces • Non-destructive

38. Activity 32.2C – Fingerprint enhancement Make a leaflet to train a new forensic scientist about the different fingerprinting methods It should include information on the following techniques: • Amido black • Superglue (cyanoacrylate) fuming • Silver nitrate Ensure you include pictures of the equipment used. Identify the types of prints the techniques are used on and from which surfaces. You could also get a before and after enhancement photo of the fingerprints.

39. PRESUMPTIVE TESTS

40. Lesson Objectives • To state the different bodily fluids that are found at crime scene • To describe the different presumptive tests for various bodily fluids • To explain the advantages and disadvantages of each test

41. What are presumptive tests? • Quick, cheap but sensitive colour change tests to check for the presence of bodily fluids • Used at crime scene or in the lab • Not 100% accurate and only test for presence – results must be confirmed in the lab by different techniques.

42. Tests for semen • Evidence of sexual contact following rape or sexual assault. • Recovered from clothes, bed sheets or from the body using swabs. • Semen contains high levels of acid phosphatase (AP). In the AP test, semen goes purple. • Confirmed in the lab using a microscope to check for the presence of sperm cells.

43. Test for saliva • Saliva is found in drinks, glasses, bottles, cans, food, bite marks, cigarettes, stamps, envelopes, chewing gum. • 99% water and 1% organic molecules. • Phadebas test to detect the enzyme amylase.

44. Tests for blood All react with haemoglobin inside red blood cells. • Leucomalachite green (LMG) – non toxic, low-sensitivity. • Kastle-Meyer Test – first used in 1903. Uses pH indicator and hydrogen peroxide and goes pink in the presence of blood. • Luminol – chemoluminescent reaction with blood that glows in the dark. Very sensitive but a possible carcinogen. Used when offender has tried to clean up evidence.

45. Activity 32.2D Bodily Fluids Produce a leaflet for a trainee SOCO that includes: • The types of bodily fluids that are found at crime scenes • A presumptive test for each fluid. • The pros and cons of each test.

46. Activity 32.2E & F - Toxicology Toxicology is the scientific study of poisons. Research the poisons arsenic and cyanide. • Produce a list of facts about each including the symptoms of their poisoning. • Describe two documented crimes that may have involved arsenic or cyanide.