Chromatography trail and investigation Essay

Published: 2020-02-20 14:32:37
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Aim: I am working for a trading standards office, a local market stall is selling some red and blue sweets that are suspected of containing illegal and possibly toxic colourings. I am going to find out using chromatography whether the dyes are illegal/ legal. Chromatography is a technique which is used for separating and identifying mixtures which are coloured for example, pigments. Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures.

It involves passing a mixture dissolved in a mobile phase through a stationary phase, which separates the analyte to be measured from other molecules in the mixture based on differential partitioning between the mobile and stationary phases. Subtle differences in compounds partition coefficient results in differential retention on the stationary phase and thus separation. Equipment List: 250ml Beaker Chromatography Paper Pencil Dyes (Red Food Colouring, Blue Food Colouring, Dylon Red, Dylon Blue) Distilled Water Capillary Tube Ruler Hairdryer Method.

1) First get a ruler and pencil and then a pencil line 1cm from the bottom of the chromatography paper. Put four crosses on the line just made. 2) Using the pencil write the name of each colour dye by the matching spot. 3) Take a Capillary tube and dip it into one of the dyes, using a clean capillary tube for each dye (We do this to make sure that they do not get mixed up). 4) We then get the chromatography paper and place it into the beaker; we then get the distilled water and fill it up to the 1cm line. 5) Now we wait and watch the distilled water separate the dye.

6) Use the hairdryer to dry the chromatography paper dry. 7) Once dry, we measure the distance travelled by each dye. We also measure the distance the water travels (the solvent front). 8) We then record the results of the experiment. Results Table: Dyes Distance Travelled (mm) Solvent Front (mm) Retention Factor (Rf Value) Red Food Colouring 10. 60, 9. 70 11. 8 0. 89, 0. 82 Blue Food Colouring 11. 15 11. 8 0. 94 Dylon Blue 5. 75 11. 8 0. 49 Dylon Red 7. 40 11. 8 0. 63 Rf = Distance Travelled By Component Distance travelled by Water Measurement Errors Ruler % uncertainty = Tolerance x 100.

Smallest Measurement 0. 5 i?? 5. 75 x 100 = 8. 69 No measurement equipment is 100% correct; any measurement equipment will have some sort of measurement error. To calculate the measurement error we need to know the tolerance and then divide it by the smallest measurement (the smaller the measurement the smaller the measurement error) then times this by 100, like the example above. Analysis At the end of my investigation I found out that 2 out of 4 of the dyes were illegal. The two dyes which were found illegal were the red and blue food colouring dyes found in the sweets.

The red food colouring dye consisted of two different colours (Pink and Orange) compared to the other which was completely red. The blue food colouring dye consisted of a cyan colour unlike the dylon blue which had a much faded and watery shade of blue. In comparison the dyes are different and should therefore be harmful and should not be placed into food products. The sweets should be banned and should stop being distributed in the shops. This can be proven by the results I have recorded from doing this experiment. Conclusion.

I have found out that chromatography can be used to find out whether a pigment is harmful or safe. The results above indicate that my analysis is correct as the Rf values are all different from one another. The red food colouring shows more than one coloured pigment giving it an R f of 0. 89 & 0. 82, whereas the dylon red shows one coloured pigment and has an Rf of 0. 63 this proves that the red food colouring is illegal. The Blue food colouring shows a different pigment which gives this dye an Rf of 11. 15; however from the dylon blue dye results it has an Rf value of 5.75 this means that the blue food colouring is also illegal.

From my results I can tell that both dyes are illegal and the sweets from the market stall should not be sold any longer as they may have toxic and harmful chemicals within them. Evaluation This experiment was very interesting; however, I myself during this experiment came across a number of problems. This first problem I came across was trying to use the capillary tubes; the dyes kept on getting mixed with one another because people were reusing the same capillary tubes to drop the dyes onto their chromatography paper.

To avoid this problem I myself would have preferred if everyone was given four capillary tubes to use for each dye instead. The second problem I faced was trying to use the dylon blue dye because it was such a faded and watery colour it was very difficult to see whether or not the dye had actually been on the paper, it was also very difficult to measure the dylon blue as it was such a faded colour. To have avoided this problem a darker dye should have been provided for the dylon blue. Besides from these two problems I think that the experiment on a whole was very interesting.

Reference: http://en. wikipedia. org/wiki/Chromatography#History.

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