Thin Layer Chromatography Report PDF

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Full report on pratccal covering thin layer chromatography- contains methods, results, tables discussion and conclusion....

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30 October 2015

Tiffany Lin Group 3B, Mon am

Thin Layer Chromatography (TLC) Aim: The aim of this experiment was to use the analytical tool, TLC, to find the composition of solutions of amino acids and combination analgesics, then use the results to determine the composition of unknown compounds. Procedure: Part 1: For the TLC of amino acids, a pencil was used (to prevent ink running through the plate) to mark 5 equidistant x’s along a 1cm horizontal line from the base of a TLC plate. 5 clean spotters were used to spot amino acid mixtures (glycine, arginine, valine, glutamic acid and an unknown mixture E) onto the plate. A developing tank with a solution of n-butanol: ethanoic acid: water (in the ratio 3:1:1) was prepared. After the spots on the TLC plate had dried, it was put in the tank while ensuring the solution did not cross the 1cm base-line and a watch glass was used as a lid to allow the atmosphere in the tank to equilibrate. The apparatus was left undisturbed for approximately 1 hour to allow the solvent to run up the plate, until it was around 1cm from the top. After the plate was removed from the solution, the solvent front was marked and the plate was dried using a hairdryer. Since amino acids are colourless, a thin layer of ninhydrin was sprayed over the plate as a stain, then baked in a 100C oven for 5 minutes, in order to observe the component spots on the TLC plate. Part 2: For the investigation on analgesics, a TLC plate was prepared as in part 1. Approximately 0.1g of powdered aspirin was measured directly into a micro test tube. Other analgesics and the unknown compound B were also roughly measured into a micro test tube. A 50: 50 ethanol/ dichloromethane solution (2cm3) was added to the test tubes and mixed for a few minutes to allow the active ingredients to dissolve. The TLC plate was spotted and left to develop as the previous experiment, but in a small volume of ethyl acetate. Once the solvent front reached approximately 1cm from the top of the plate, it was removed from the solution and the solvent front was marked and the plate was dried. The plate was placed under a UV lamp so the position of the spots could be observed. During both procedures, precautions of contaminating the TLC plates were taken for it to run successfully. These included using tweezers to handle the plates, clean apparatus to be used at all times and one spotter to be used per sample. The apparatus used in the amino acid experiment was rinsed with water however, the apparatus used in the analgesic investigation had to be emptied into the non-halogenated waste bottle and then rinsed with acetone.

30 October 2015

Tiffany Lin Group 3B, Mon am

Results: The Retention Factor values, Rf, were calculated from the TLC plates for each sample in both investigations. Part 1: Amino Acid Rf Value Glycine 0.28 Arginine 0.12 Valine 0.46 Glutamic acid 0.30 Mixture E 0.46 Table 1. Rf values (2 significant figures) for the amino acid experiment. Part 2: Analgesic Rf Value Ibuprofen 0.85 Aspirin 0.76 Paracetamol 0.59 Caffeine 0.19 Unknown B 0.59` Table 2. Rf values (2 significant figures) for the analgesic investigation. Calculation example: Distance run by glycine spot = 1.9cm Distance run by solvent front = 6.9cm Rf (Glycine) = Distance run by component spot Distance run by solvent front = 1.9 6.9 = 0.28

30 October 2015

Diagram of TLC plates: Part 1:

Tiffany Lin Group 3B, Mon am

Part 2:

Part 1 shows that mixture E has 3 spots with the same R f values as glycine, glutamic acid and valine which shows that it is composed of these 3 amino acids. Part 2 shows that unknown B has 2 spots with the same R f value as paracetamol and caffeine, therefore it contains these 2 components. Conclusion: In conclusion, TLC can be used to identify the components of a compound if its R f value is compared with the Rf value of a known compound. In part 1, mixture E is composed of glycine, glutamic acid and valine. In part 2, unknown compound B is composed of paracetamol and caffeine.

30 October 2015

Questions: 1. Structures of a) Glycine

b) Arginine

c) Valine

d) Glutamic acid

Tiffany Lin Group 3B, Mon am

30 October 2015

Tiffany Lin Group 3B, Mon am

2. Although caffeine is not an analgesic, it is included in analgesic preparations because it acts as an assistive agent which increases the efficacy of analgesics....