Mixtures are made up of two or more components with different properties. Also, there are many methods that are used to separate mixtures to their basic components. In the case of liquids, these methods are known as chromatography. This is done to separate the mixture into its components based on its relative ability to move through the stationary phases (fixed phase) through the mobile phase. Some components of the mixture move more easily, while others are reluctant to do so. This causes the mixture to separate into groups of different components.
Steps
Part 1 of 3: Create a sample
Step 1. Make or buy a chromatography strip
A chromatography strip is a strip of material through which the mixture of mobile phase, a liquid or a gas, travels. This strip serves as the stationary stage so that you can observe the speed at which the different components move in the mobile phase. You can buy specially formulated chromatography strips for superior results, but if you want to do simple chromatography, you can do it yourself. To do this, cut a coffee filter into strips about 1 inch (2.5 cm) wide and 5 to 6 inches (12-15 cm) long.
If you don't have a coffee filter, you can use paper towels or any other type of paper
Step 2. Place a colorful line near the bottom of the strip
Measure about 1 inch (2.5 cm) from the bottom of the strip. In this experiment, you will need to separate the components of a marker. To do this, use a black marker to draw a straight line across the width of the strip. Make sure the strip is long enough so that you can dip the bottom of the paper without reaching the line.
Some people use a point instead of a line. This will work just as well, although the bands will not be as clearly defined with this method
Step 3. Fix the chromatography strip in a vertical position
Use clothespins to fix the strip in an upright position so that you don't need to hold it in the water yourself. It should be hung in such a way that the side with the drawn line is close to the ground. Make sure to position the clothespin as high as possible on the strip while still holding it tight. Placing it too low could interfere with the risers.
In addition to the clothespins, you can also hang the strip using paper clips, tape or any other mechanism that you consider appropriate
Part 2 of 3: Introducing a solvent
Step 1. Pour water into a cup
When performing simple chromatography, the solvent (the liquid that carries the mobile phase through the stationary phase) will be water. Add some water to a clear cup or glass. You will only need enough for the strip to absorb, so you will only need a few ounces.
Step 2. Dip the chromatography strip in the water
While holding the chromatography strip upright, dip it into the water. Make sure you have a fixed object to hold the strip in place, as this process can take a long time. The bottom of the strip should be submerged, but not up to the marker line. If you dip this line by mistake, discard the strip and make another.
For example, you can use a pencil placed on the top of the glass to hook the clamp that holds the strip. This way, the strip will hang down and barely come into contact with the water
Step 3. Wait patiently
As the water moves up the strip, it will carry the different compounds on the marker. The lighter compounds (the smallest) will travel faster, while the heavier (the largest) will travel slower. This will separate the compounds into "bands" based on their size. However, keep in mind that it is a slow process. Watch the strip until you see that the water reaches about 1 inch (2.5 cm) from the top.
- The exact time it takes for the water to reach this height will depend on the type of strip you use.
- Do not move the cup or pencil after dipping the strip. Avoid generating any kind of agitation that affects the result by diffusion of the bands.
Part 3 of 3: Observe the bands
Step 1. Take out the strip
Place it on a smooth surface and wait for it to dry.
Step 2. Count the bands you see
After removing the strip from the water, the bands should stay in place. This will allow you to count how many different bands are visible, giving you a rough idea of how many different sized compounds are in the marker ink.
Step 3. Pay attention to the color of each band
The black marker ink is made from several different pigments, each of which have their own unique colors. By separating them into bands, these will have the color of each individual pigment. By looking at the color of each band, you can analyze which pigments were used to create the black ink for the marker.
Step 4. Score the bands from the top to the bottom of the strip
Write down the colored bands based on the distance they traveled. Bands near the top are for the lighter compounds, while bands near the bottom are for heavier compounds. You could probably also notice a top-down color trend. Generally, the lightest colors are the smallest compounds and thus move further up the strip. For their part, the darker colors stay closer to the bottom because they are usually the heaviest compounds.
- The relationship between the distance a compound traveled (Dc) and the distance a solvent traveled (Ds) is known as the Rf value. You can calculate the Rf value of any band by dividing the distance the band traveled from the original line by the distance the solvent traveled from the same line.
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For example, if you have a band that traveled about 2 cm beyond the drawn line, while the solvent reached about 5 cm above it, you can use the following equation: Dband/ Dsolvent = Rf. In this example, the equation would be written like this:
- Rf = 2 cm / 5 cm
- Rf = 0.4
Advice
- If you want to do this more scientifically, you can buy chromatography paper, which is similar to a coffee filter, but creates a much more obvious and less blurry stripe of colors if used properly. You can buy it at various stores that sell laboratory equipment.
- Try different colored markers and see which one comes to the top first, which will create the prettiest pigment strip.
- Chromatography is done in real scientific laboratories for a number of different reasons, and it can get very complex. Chromatography encompasses a wide variety of scientific tests and is not limited to this method.
- Before doing this experiment, make sure the marker is water soluble. A permanent marker is usually not helpful in this case.
- Why does it work? Pigments of different colors have different shapes at the molecular level. These move differently along the paper due to the difference in the relative affinity of the components towards the mobile and stationary phases. This is also technically known as a distribution or partition coefficient. A long stretch of pigments arranged in an organized line will form with the most similar colors located close to each other.
Warnings
- Avoid submerging the mark in the filter, as that will ruin the chromatography.
- Let the mark dry.