For my chemistry project, I performed two types of experiments. The first was investigating two kinds of chromatography -- paper chromatography using chromatography paper and coffee filters and thin-layer chromatography (TLC). With the paper chromatography, I tried four different solvents to see which one worked the best with each color of food dye. For the TLC, I used the solvent provided with the kit. The second was experimenting to find a method for extracting food dyes from the coating of candy bits that I had chosen.
When I started my experimenting, I used chromatography paper that I had purchased along with liquid food colors and paste food colors. As a solvent I used distilled water. Some of the separations were not very good. My aunt suggested using coffee filters instead since they are thinner and might give better separations. Also, after e-mailing people and doing more research on the Internet, I decided to try three other solvents: white vinegar, household ammonia, and a 5% NaCl solution with distilled water. I experimented using all four of my solvents with each liquid food color and paste food color and the two types of paper. Whenever possible, I calculated the Rf values for the five food dyes in all the food colors. The purpose of this was to have known values to compare my unknowns to later. I have given descriptions of the experiments that I have done below. These include how to do the experiments with the four solvents and the coffee filter paper and chromatography paper.
My other experiments focused on learning how to get a concentrated amount of
the dye from the candy shell. When doing my project, the hardest part was
extracting the dyes. I first tried dissolving the candy coating in distilled
water. This did not give a dye solution that was concentrated enough because the
solution just disappeared on both the coffee filter and the chromatography paper
and I could not see any separate colors using any of the solvents. The method I
tried next was from an experiment entitled "Candy
Chromatography" by John Hnatow. This method worked very well and is
also summarized below.
1) Cut several strips of chromatography paper. Each strip should be about 28 cm (11 inches) long and 2.54 cm ( one inch) wide. Use scissors to cut a triangular tip at the bottom of the strip. Do not make the tip too long; it should be about two cm. The coffee filters should be cut into squares about 13 cm on each side.
2) Pour enough solvent in the beaker to cover the bottom and be about one-half centimeter deep. Put the beaker into the large saucer. Put the same solvent that is in the beaker into the large saucer. Use enough to completely cover the bottom of the saucer. Put a capped soda bottle over the beaker and into the large saucer, making sure that it touches the solvent in the bottom of the saucer. This is done to seal the experiment from the outside which prevents the paper from drying out too fast and to make sure the chamber is saturated by the solvent.
3) Using the pencil, draw a line about one centimeter up from the top of the tip on the strip of chromatography paper. Using a toothpick, put very small dots of dye along the line you just drew. You can put two or three dots on the chromatography paper strip. If you are using coffee filters, draw a line about one centimeter from the bottom of the filter. You can put up to eight different colors on the coffee filter paper but make sure that these are in the center section of the coffee filter paper. You do not want them close to the edge of the paper. Make sure to use a different toothpick for each different color, and keep the color in a small tight dot on the paper; if the color spreads into a large area, throw that paper away and start over because this will ruin the experiment.
4) Chromatography Paper: Place a piece of tape, about
20 centimeters long, along the top of the chromatography paper. Put the paper
strip through the top of the soda bottle and into the beaker just so the tip is
in the solvent. Secure the tape to the sides of the soda bottle to hold the
paper in place. Replace the cap on the soda bottle. The solvent should not reach
above the line you drew with a pencil. If it does then pour out some of the
solvent, and throw the chromatography paper away and start over. Do not let the
paper touch the sides of the beaker. If it does move it so that it does not
touch.
Coffee Filter: Wrap the coffee filter into a cylinder so that the opposite sides overlap and so the line of the dots of color are still parallel to the horizon. Use a paper clip to keep the ends together. It should look like a column. Remove the soda bottle and put the coffee filter paper into the beaker. The solvent should not reach above the line you have drawn. If it does take out the coffee filter, pour out some solvent, throw the coffee filter away and start over. The coffee filter should not touch the sides of the beaker. If it does, fix it so that it doesn't. Place the capped soda bottle back over the beaker.
5) Keep an eye on the chromatography paper or coffee filter. You should be able to see the colors separate as the solvent climbs up the paper. Remove the paper when the colors stop moving or when the solvent reaches about a centimeter from the top of the paper, whichever occurs first. The solvent front should be well above the highest color to be sure that the colors have stopped moving. Put the paper on a dry clean surface, preferably on a white paper towel. Draw a line with the pencil where the solvent front stopped. Let the paper dry.
6) Now you can calculate the Rf values.
Note:
For this part of my experiment, I used a Lab-Aids Thin-Layer Chromatography Kit that I purchased from Nasco Science . The solvent and the thin-layer cells that I used were part of the kit. When using Thin-Layer Chromatography, I would suggest using a kit with pre-made thin-layer cells and a solvent to use with these cells. While researching, I learned that sometimes solvents are prepared to work with a certain thin-layer cell. Changing the solvent can sometimes cause the experiment not to work. This is not always true, but just to be safe, I would use an already prepared solvent that was provided to work with the thin-layer cells that you have.
1) Pour the solvent into a developing chamber to a depth of no more than 1 cm and close the lid. This will allow the chamber to become saturated.
2) LIGHTLY draw a line across the bottom of the cell no more that two cm from the bottom edge.
3) Using a capillary tube, apply a sample of a dye to the cell on the line you just drew. Use a new, clean,capillary tube for each dye. Touch the capillary tube lightly to the cell but do not push on the cell. Keep the spot very small. You can put up to four spots of the dye on a 2.54 cm wide cell.
4) Place the cell in an upright position, leaning against the back, into the developing chamber. Close the cap tightly. Do this as quickly as you can because you want to keep the chamber saturated.
5) Watch the solvent front advance up the cell. When it is about 1 cm from the top of the cell remove the cell from the chamber. Put it on a clean dry surface. Immediately, use a pencil to lightly draw a line where the solvent front stopped. Also, look carefully at the colors and their locations because the colors will lighten up as the solvent evaporates; you may want to mark with a pencil the center of each color band, especially if it is a light color.
6) You can now calculate the Rf values
1) Place a test tube containing 10-15 cm length of white woolen yarn and 10-15 mL of household vinegar in a boiling water bath and heat for 4-5 minutes. This will remove any fluorescent dyes which might interfere with the separation of the FD&C dyes. After cooling, remove the yarn from the vinegar and let it drain.
2) Put five to six candy pieces in a test tube with enough white vinegar to cover them. Heat the tube in a boiling water bath until the colored coating dissolves and the candies are a white color. This will happen fast so be careful not to dissolve any of the white layer under the colored layer or the interior of the candy.
3) Carefully decant the solution, which now contains the candy dyes, into a clean test tube. Make sure not to transfer any sediment.
4) To extract the dye from this solution, place the yarn and 3 mL of vinegar into the test tube containing the dye solution. Heat this tube in the boiling water bath for about 5 minutes with occasional stirring. When all the dye has been extracted, the solution will be a milky white color and the yarn will be the color of the dye. Remove the yarn and rinse it in tap water.
5) To release the extracted dyes, place the yarn and about 5 mL of clear household ammonia in a clean test tube. Mix it with a stirring rod and test the resulting solution with red litmus paper to make sure that it is basic. If it is not, then add more ammonia until it is.
6) Heat the tube containing the yarn and ammonia in a
boiling water bath for about 5 minutes or until the yarn has faded, with
occasional stirring to release the dyes. Remove the yarn and pour the solution
containing the dyes into an evaporating dish. Heat the evaporating dish gently
to concentrate the solution. Stop just short of dryness. If all the liquid
evaporates, add a drop or two of distilled water and stir.
Project researched and
documented by Ann VanBlaricum Disclaimer: These pages were written in 1997
while the author was a sophomore in high school taking AP Chemistry. Hence, the
author is not an expert on this subject, she cannot vouch for the accuracy or
currency of these data or the links.
Questions or problems regarding this web site should be
directed to Ann@DoggedResearch.com.
Copyright © 1997
Ann VanBlaricum
All rights reserved.