What is Chromatography?
The word chromatography describes any method that can separate components of a substance by dissolving the substance in a mobile phase (a liquid or gas, called a “solvent”), then passing that mobile phase through a stationary phase (a solid, like paper). The separation happens because as the various components are carried by the mobile phase, they begin to interact with the stationary phase. If a component is very attracted to the stationary phase, it will slow down and not travel as fast as the rest of the mobile phase because it is spending a lot of time “stationary” on the stationary phase instead of being “mobile” in the mobile phase. Components that are not attracted to the stationary phase will travel as fast as the mobile phase. Therefore, when you stop the flow of the mobile phase, the components will be separated based on how much they have interacted with the stationary phase, which is related to how far they have traveled.
For an analogy, say you had a bunch of strawberries in a row on the floor (your stationary phase) stretching across the room. Then, you let three babies (the components in the mobile phase) crawl along the row of strawberries. A baby who doesn’t like strawberries will just crawl on by and not eat anything. This is kind of like a component traveling with the mobile phase that has no attraction to the stationary phase. A baby who really likes strawberries will stop and eat almost every one. This will slow down their pace compared to the other baby. The third baby kinda likes strawberries but not much, and stops to eat only some of them. That baby will have a pace somewhere in between the two other babies. If you freeze frame the babies before the fastest one reaches the end of the strawberries (stationary phase), you have just separated the babies based on their attraction to strawberries. In chromatography, you separate molecules based on their attraction to a stationary phase, where instead of strawberries, you use things like silica or antibodies.
Flower Petal Chromatography
- flower petals
- household solvent like acetone (some types of nail polish remover), ethyl acetate (other types of nail polish remover), or isopropanol (rubbing alcohol). I recommend acetone.
- Mortar and pestle (or some other way to crush the petals, like a spoon and bowl, or rock and bowl) Fox Run 6240 Porcelain Mortar & Pestle, White
- Filter paper (the kind I have and is available on Amazon Filter Paper, Qualitative, Medium, 18cm) (*coffee filters will not work well for this project)
- A glass container like a mason jar or drinking glass
- Something to cover the top of the glass container (like a coaster)
1. Gather a few flower petals of varying colors.
using a pencil and tape to suspend the paper. The paper should not touch the glass on the sides, otherwise the solvent will just run up the side of the paper.
Put the petals in the mortar and add about 1/2 tsp of
won’t get defined bands.)
- Try several different solvents to see how the chromatograph changes.
- Do this procedure with different vegetables and compare the results. If you want to get technical, you can calculate the retardation factor (Rf value) by measuring how far a component traveled from the origin (that you originally marked with pencil) and dividing that by how far the solvent front traveled from the starting point. Take that number to two decimal places, then compare Rf values of similar colors from different vegetables to serve as evidence that they are the same compound. (To compare Rf values, you have to use the same mobile phase/ stationary phase combination to be valid, so don’t use different solvents here.)
- Do this procedure in the fall with different colored leaves from the same tree. Do green leaves have orange and red compounds in them? Do orange and red leaves have green compounds?