Introduction to chromatography and spectroscopy

1. Introduction to chromatography and spectroscopy • Using chromatography and spectroscopy to solve a mystery • Seeing in 3D

2. Thin-layer chromatography (TLC) Used to investigate the purity and identity of samples • Stationary phase: silica plate • Mobile phase: solvent As the solvent rises up the plate, different compounds move up the plate at different speeds • Polar compounds move slowly • Lipophilic compounds move quickly UV lamp often used to visualise the compounds on the plate

3. Assessing purity Pure compound 1 Impure compound 1 impurity

4. Identifying unknown samples Compound A Compound B Unknown How would you confirm that the unknown was compound B?

5. Identifying unknown samples Compound A Compound B Unknown Unknown Mixed Mixed Consistent with unknown being compound A

6. How does spectroscopy work? • Light is a mixture of different colours (wavelengths/frequencies) Infra-red Ultra-violet

7. How does spectroscopy work? • Different materials absorb different parts of the spectrum This reflected light tells us something about the material Absorbs everything but blue and red

8. Infra-Red (IR) spectroscopy • In IR spectra, regions of light are absorbed by specific parts of the molecule. For example IR light 1715cm-1 The C=O bond of a ketone absorbs light in the region of 1715cm-1 so that the emerging IR light has this piece of its spectrum missing

9. Infra-Red (IR) spectroscopy • Every compound has a unique IR spectrum that tells us something about the structure IR light Unknown compound http://www.le.ac.uk/spectraschool/sias/UV%20poster.pdf

10. Solving a mystery – Part 1 • A dead body has been found • 2 empty bottles of 3 painkillers found at the scene • Aspirin • Paracetamol • It is suspected that the victim took an overdose of one of these • Using the Thin-Layer Chromatography (TLC) and Infra-Red (IR) spectroscopy, can you work-out which painkiller is most likely to have led to the death of the victim?

11. Safety Safety glasses and gloves to be worn throughout Painkillers Aspirin and paracetamol are active medicines. Do not ingest. TLC tank solvent: diethyl ether dichloromethane tetrahydrofuran Solvent for dissolving the painkillers: ethanol Solvent for washing the IR sodium chloride plates Acetone Use of UV lamp to observe TLC plates Do not inhale the solvent or allow it to contact your skin Diethyl ether and tetrahydrofuran are highly flammable Ethanol is highly flammable Acetone is highly flammable • UV light is harmful to eyes and skin. • Do not look directly at the light or place your hands under the light

12. Which one could have killed the victim? Aspirin Paracetamol

13. Solving a mystery – Part 2 • We now know that aspirin was present in the victim’s blood. • What we don’t know is whether there was enough in the blood to kill the victim. • Therapeutic concentrations: <300mg/L • Severe overdose: >750mg/L • We are going to use visible spectroscopy to reach a conclusion http://www.le.ac.uk/spectraschool/sias/UV%20poster.pdf

14. Solving a mystery – Part 2 • How much aspirin was present in the victim’s blood? • What was the likely cause of death?

15. Colour filters and 3D visualisation • In IR spectra, regions of light are absorbed by specific parts of the molecule. IR light 1715cm-1 The C=O bond of a ketone absorbs light in the region of 1715cm-1 so that the emerging IR light has this piece of its spectrum missing

16. Colour filters and 3D visualisation • A colour filter on a camera works in a similar way It absorbs all the colours in white light apart from red, making everything look red white light As a result, red/orange objects are difficult to see with a red filter

17. Colour filters and 3D visualisation Here is a light orange circle and a light blue square What do you expect to see when you look at this through a red filter? What do you expect to see when you look at this through a blue filter? (e.g. 3D specs, Quality Street wrappers) What about a red filter for one eye and a blue filter for the other?

18. Colour filters and 3D visualisation When you do the same thing with shapes that are similar and are almost on top of one another, something strange happens What do you think is happening? How can this help us think about the shape of molecules?

19. http://www.dddesign.com

22. We draw them flat but they do have 3D shape Aspirin Paracetamol http://www.3dchem.com/molecules.asp?ID=157 http://www.3dchem.com/moremolecules.asp?ID=9&othername=Paracetamol

23. Aspirin

24. Paracetamol