Abstract
Quick, what is your favorite color of M&Ms® candy? Do you want to know what dyes were used to make that color? Check out this science project to find out how you can do some scientific detective work to find out for yourself.Summary
Andrew Olson, PhD and Sandra Slutz, PhD, Science Buddies
Sources
This project idea is based on:
- Helmenstine, A.M.( 2007). Candy & Coffee Filter Chromatography. Retrieved July 17, 2007.
Recommended Project Supplies
Objective
Use paper chromatography to see which dyes are used in the coatings of your favorite colored candies.
Introduction
Have you ever had a drop of water spoil your nice print-out from an inkjet printer? Once the water hits the paper, the ink starts to run. The water is absorbed into the fibers of the paper by capillary action. As the water travels through the paper, it picks up ink particles and carries them along. This same process that spoils a perfect print-out can also be put to good use. There is even a name for it: paper chromatography. To learn more about paper chromatography, you can continue reading and/or watch the video below. The video gives an overview of what paper chromatography is, shows how it is done, explains the separation processes involved, and also provides tips and tricks for troubleshooting your experiment.
Chromatography is a group of techniques, including paper chromatography, that are used to separate the various components in a complex mixture or solution. In each chromatography apparatus there is generally a mobile phase, which is a fluid that runs along the stationary phase, and a stationary phase, that stays stationary while the mobile phase moves through. For example in paper chromatography, the mobile phase could be rubbing alcohol, while the stationary phase is the paper, or more precisely the water that is adsorbed to the paper. The mobile phase is also called the solvent.
How does the chromatography setup separate the components in the solution? The components ideally move at different speeds as they travel through the stationary phase. This is done by adjusting the mobile and stationary phases so that individual components of the mixture interact with both phases differently. Properties such as solubility, polarity, electrical charge, or other chemical properties usually determine how the components within a mixture are separated from each other. In paper chromatography, different pigments can be separated out from a solution based on the same principles. A pigment that interacts more with the mobile phase, for example because it is more soluble in the solvent than another pigment will generally travel farther because it will be easier for it to dissolve in the mobile phase and be carried with the mobile phase along the stationary phase. A pigment that is less soluble in the solvent, or interacts more with the stationary phase than the mobile phase, will generally travel a shorter distance. Because different pigment molecules have different chemical properties, they are separated from each other on the chromatography paper, as shown in Figure 1.
A homemade paper chromatography testing box is made from a tall box with a lid. A dowel spanning the width of the box is placed near the top to allow a binder clip to hold a paper strip that has been marked by colored pigments. The paper strip is long enough to reach the bottom of the box where there is a small pool of solvent. As the solvent is absorbed by the paper and moves upward it brings some of the colored pigment markings with it.
Figure 1. Paper chromatography. Molecules are separated from each other, depending on how fast they migrate with the solvent up the chromatography paper. (Wikipedia, 2008.)
In paper chromatography, you can see the components separate out on the chromatography paper and identify the components based on how far they travel. To do this, we calculate the retention factor (Rf value) of each component. The Rf value is the ratio between how far a component travels and the distance the solvent (mobile phase) travels from a common starting point (the origin). For example, if one of the sample components moves 2.5 centimeters (cm) up the paper and the solvent moves 5.0 cm, as shown in Figure 2 below, then the Rf value is 0.5. You can use Rf values to identify different components as long as the solvent, temperature, pH, and type of paper remain the same. In Figure 2, the light blue shading represents the solvent and the dark blue spot is the colored solution sample.
Diagram of a paper chromatography strip shows how marker ink travels up the length of a paper strip when the strip absorbs a liquid solvent. An origin line marks the original position of the ink and the solvent is colored blue so the distance the solvent travels up the paper strip can be measured. In the diagram, solvent traveled 5 centimeters, while the sample traveled 2.5 centimeters from the origin line.
Figure 2. For each compound, an Rf value is calculated based on how far it traveled along the stationary phase. In paper chromatography, Rf values are used to compare different components to each other.
Rf values are calculated by looking at the distance each component travels on the chromatography paper compared to the distance traveled by the solvent front. This ratio will be different for each component due to its unique chemical properties.
When measuring the distance the component traveled, you should measure from the origin (where the middle of the spot originally was) and then to the center of the spot in its new location. To calculate the Rf value, we then use Equation 1 below.
Equation 1:
In our example, this would be:
Note that an Rf value has no units because the units of distance cancel.
You can probably now imagine how chromatography can be used to separate (purify) specific components from a complex mixture and identify chemicals, for example crime scene samples like blood, drugs, or explosive residue. Highly accurate chromatographic methods are used for process monitoring, for example to ensure that a pharmaceutical manufacturing process is producing the desired drug compound in pure form.
In this food science project, you will use the Rf value to compare the "unknown" components of colored candy dyes with the "known" components of food coloring dyes. Since there are only a small number of approved food dyes, you should be able to identify the ones used in the candies by comparison to the chromatography results for food coloring.
Terms and Concepts
- Capillary action
- Paper chromatography
- Solution
- Mobile phase
- Stationary phase
- Solvent
- Solubility
- Polarity
- Retention factor (Rf)
Questions
- Why do different compounds travel different distances on the piece of paper?
- How is an Rf value useful?
- What is chromatography used for?
Bibliography
- United States Geological Survey (USGS) (2018). Capillary Action and Water. Retrieved March, 2022.
- Science Buddies. (n.d.). Paper Chromatography Resources. Retrieved January 14, 2018.
- U.S. Food and Drug Administration. (2013, March 13). Overview of Food Ingredients, Additives & Colors. Retrieved March 21, 2013.
- Waters Corporation Staff. (2012). High Performance Liquid Chromatography. Retrieved November 29, 2012.
Materials and Equipment 
Recommended Project Supplies
- Candy Chromatography Science Kit, available from our partner
Home Science Tools.
You will need these items from the kit:
- Chromatography paper strips; at least 15. The kit contains 20 strips; additional chromatography paper can be purchased separately from our partner Home Science Tools.
- 100 mL beaker
- 500 mL beaker
- Mini binder clips (2)
- Wooden splints (2)
- Food coloring; red, green, and blue
- M&Ms and Skittles (at least 15)
- We recommend testing three different colors, and testing each color with five candies that are the same type (e.g., five red M&Ms, five brown M&Ms, and five blue Skittles).
- Pipette
- Note: This kit contains additional items to do other chromatography science projects. See the kit instructions page for details.
- You will also need to gather these items, not included in the kit:
- Scissors
- Ruler; metric
- Pencil
- A clean plate or plastic lid
- Measuring cup; 4 cup volume
- A 1 cup volume measuring cup and a container large enough to hold 4 cups of water can be substituted.
- 1/8th teaspoon (tsp) measuring spoon or 1/4th tsp measuring spoon
- Salt
- Water
- Lab notebook
Disclaimer: Science Buddies participates in affiliate programs with Home Science Tools, Amazon.com, Carolina Biological, and Jameco Electronics. Proceeds from the affiliate programs help support Science Buddies, a 501(c)(3) public charity, and keep our resources free for everyone. Our top priority is student learning. If you have any comments (positive or negative) related to purchases you've made for science projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org.
Experimental Procedure
- Do your background research so that you are knowledgeable about the terms, concepts, and questions listed in the Background tab.
-
Choose three colors of candies you want to test.
- For example, you could test red M&Ms®, brown M&Ms®, and blue Skittles®.
- Cut each chromatography paper in half (length-wise) to make approximately 2 centimeters (cm) wide by 7.5 cm long strips. You will need at least 30 chromatography strips.
- Use a pencil to lightly label which candy color or food coloring will be spotted on each paper strip. Label 5 chromatography strips for each candy color and 5 strips for each food coloring (red, green, and blue). Tip: do not use a pen for writing on the strips: the ink will run when the solvent passes through the strips.
-
Draw a pencil line 1 cm from the edge of each strip of paper, as shown in Figure 3 below.
- This will be the origin line or baseline.
- You will spot the candy color for each strip right on this line, as shown in Figure 3.
Figure 3. Each chromatography strip will have an origin line (baseline). The dye to be tested will be spotted in the middle of the origin line.
-
Next you need to extract some dye from each candy you wish to test.
- Fill the 100 mL beaker with some water.
-
Use the pipette to put a single drop of water in the clean plate or plastic lid as shown in Figure 4 below. Set one candy in the drop of water.
- Tip: If you use too much water, the dye will not be concentrated enough to see on the chromatography strip.
- How to use the pipette: Squeeze the pipette at its widest point. While continuing to squeeze, insert the narrow end into the beaker of water. Release the wide end and the pipette will fill with water. Put the narrow end of the pipette directly over the plate or plastic lid. Gently squeeze the wide end of the pipette to release one drop of water.
- Leave the candy in the drop of water for three minutes to allow the dye to dissolve.
- Remove the candy, then dip a pipette tip, or clean wooden splint tip, into the now-colored drop of water.
- Spot the candy dye solution onto the chromatography strip by touching the pipette tip, or a wooden splint, to the strip, right in the center of the origin line as shown in Figure 5 below.
- Allow the spot on the strip to dry completely (this should take approximately 1 minute).
- Repeat steps 6e to 6f 3–5 more times. You want to make sure to have enough dye on the chromatography strip so that you can see the dye components when they separate out on the paper.
- Repeat steps 6b to 6g with four more strips and four new candies that are the same type and color (e.g., all red M&Ms®).
Figure 4. To extract the candy dye, leave a piece of candy in a single drop of water for three minutes. When you remove the candy, a puddle of dye will be left behind.
Figure 5. Spot the extracted candy dye onto the paper chromatography strips using the tip of a wooden splint or a pipette.
- Repeat step 6 for the other two colors of candy you want to test. In the end you should have 15 spotted chromatography strips—5 for each colored candy type.
-
You also need to prepare chromatography strips with food coloring dyes.
- These will be your known compounds, with which you will compare the "unknown" candy dyes.
- For each food coloring color put a drop of coloring on a fresh plate or plastic lid.
- Dip a clean wooden splint tip or a pipette into the drop of food coloring.
- Spot the food coloring onto a chromatography strip by touching the wooden splint, or pipette, to the strip, right in the center of the origin line.
- Repeat steps 8c to 8d until you have 15 chromatography strips spotted with food dye— 5 red, 5 blue, and 5 green. Also repeat step 8b if needed.
-
Prepare a 0.1% salt solution for the chromatography solvent.
-
Add 1/8 teaspoon of salt to 4 cups of water (approximately 1 gram [g] of salt to 1 liter [L] of water).
- If you only have a ¼ teaspoon measuring spoon fill that spoon half full of salt— that will be close enough for this project.
- Shake or stir until the salt is completely dissolved.
-
Add 1/8 teaspoon of salt to 4 cups of water (approximately 1 gram [g] of salt to 1 liter [L] of water).
-
Pour a small amount of the salt solution into the 500 mL beaker.
- Clip two of the prepared chromatography strips to a wooden splint. Make sure the two strips do not touch each other or the beaker and that their bottoms are aligned. Rest the splint on top of the beaker so that the strips hang straight into the beaker.
- If necessary, add more of the salt solution. The goal is to have the end of the chromatography strips just touching the surface of the solvent solution (salt solution), as shown in Figure 6 below.
Figure 6. Your chromatography setup should look similar to this example. The edge of the chromatography strips should just barely touch the solvent.
- Let the solvent rise up the strip (by capillary action) until it is about 0.5 cm from the top then remove the strip from the solvent. Depending on the chromatography paper, this can take anywhere from 30 minutes to several hours. Regularly check on your chromatography strip and the solvent front— if you let it run too long the dye may run off the paper and become distorted.
- Be patient and do not take the paper strip out of the solvent early. The longer you keep the paper strip in the solvent, the better your separation will be!
- Use a pencil to mark how far the solvent rose.
-
Allow the chromatography strip to dry, then measure (in centimeters) and calculate the Rf value for each candy color (or food coloring) dye component. Record your results in your lab notebook.
- Tip: Use Equation 1, which is given in the Introduction, for calculating the Rf value.
-
Repeat steps 10–13 until you have run all of the chromatography strips.
- Each time you run the experiment make sure there is enough solvent in the beaker. The chromatography strips should be just touching the surface of the solvent. Add more solvent (salt solution) as needed.
- Using the five repeated strips for each candy color (or food coloring), calculate the average Rf for each dye component.
Analyzing Your Results
- Create a data table like Table 1 for each candy type and color or food coloring that you tested in your lab notebook.
| Candy Type/Color or Food Color: | |
|---|---|
| Component Color | Component Rf value |
| Total number of components: | |
- Record all your results for one candy type and color or food color in a different data table.
- Make a pie chart for each candy type and color as well as food color. The pie chart should show the number of components (one wedge per color), the color of each component (label and color each wedge appropriately), and the Rf value for each component (part of the wedge's label).
- Compare the Rf values for the candy colors and the food coloring dyes. Can you identify which food coloring dyes match which candy colors? How many dye components does each candy color have? Do your results make sense to you?
- Hint: You can look at the ingredients on the packaging to see which food coloring dyes may have been used to help you answer these questions.
- Note: It is possible that other components in the candies may affect how well the food coloring dyes travel through the paper. Why do you think this might be? (Hint: Think about solubility or polarity, and re-read this part of the Introduction.) If you have unexpected results, do you think this might help explain them?
Troubleshooting
For troubleshooting tips, please read our FAQ: Candy Chromatography: What Makes Those Colors?.
Ask an Expert
Variations
- For a chromatography experiment on separating the ink components from markers, see the Science Buddies project Paper Chromatography: Is Black Ink Really Black?
- Try this project with a variety of candies— for example, does the red in Skittles® look the same as the red in M&Ms® when processed with chromatography? Is the average Rf value nearly the same? Look in the ingredients on each package to try and determine if the same dyes were used.
- You could try this science project again but this time compare using different kinds of solvents (e.g. pure water, vegetable oil, isopropyl rubbing alcohol, etc.). Does a dye travel different distances depending on the solvent you use? What do you think this tells you about the chemical properties such as solubility or polarity of that dye?
- Do the dyes you tested in this science project travel differently on different kinds of paper? You could repeat this project to try and find out. For example, you could compare lightweight paper towels, heavyweight paper towels, white coffee filter papers, and other types of filter paper. Do they all work? Do some work better than others? Why do you think this is?
- For more advanced chromatography experiments, see these Science Buddies projects:
Frequently Asked Questions (FAQ)
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