Thin Layer Chromatography and Color Markers, or Chromatography for Kids.
In this experiment we'll use home made thin layer chromatography plates to analyze black pen ink and compare components of this ink to other colored marker inks.
Our hypothesis is that black ink is actually a composition of many color inks and we can separate them and find colored markers correspondent to each ink contained in the black marker.
We'll conduct our ink chromatography experiment in two stages. In stage one we'll find if black color ink is a combination of many inks. If this is true, in stage two we'll try to find if components of black marker are the same as the inks of other colored markers.
For this experiment you'll need (Materials and equipment):
- Water based marker pens. (our specimens)
- Home made thin layer chromatography plates.
- Small glass bowl or jar.
- Notebook for results.
- Photo camera (optional).
- Define origin line on TLC plate. Unlike
chromatography you should NOT draw the line with the pencil,
will break the stationary phase layer. However you can make little
marks on each side of the plate which would define origin line.
- Draw small dot on the origin line of the plate. Be very careful and try to make sure that spot is small and accurate. Inks are readily absorbed by the plate and tend to produce big ugly spots. Such spot will overload the plate and result in the bad separation of pigments. Usually very light touch of marker is enough to produce nice small spot.
- Pour solvent in the solvent chamber. We
did several tests with
different thin layer chromatography plates and different solvents. We
used chalk and starch plates. The amount of solvent should be pretty
small – it should barely cover the bottom. There should be enough
solvent to touch the base of the plate with stationary phase, but not
enough to wash the sample ink stains! As solvents we used:
- MrMuscle (glass cleaner, non colored).
- Nail Polish remover.
- Ethanol + water mix
- Solvent chamber should pe placed on horizontal surface. Very accurately put chromatography plate in the solvent chamber. It should be done in one quick and smooth movement. And again, it's very important that solvent not touching the sample. Cover chamber with lid. It's not necessary to cover chamber if you use water as solvent, but important if you deal with more volatile and smelly solvents such as nail polish remover, vinegar, turpentine, etc.
- Wail a little more. Check yourchromatogram from time to time. You'll see how solvent front moves through the start line up the plate. Watch capillary force in action. Depending on the solvent it takes from 5 to 20 minutes for solvent to make it 2/3 up the plate made of microscopic slide. The strength of capillary force depend on type of stationary phase and surface tension of the solvent. (And surface tension is function of polarity of the solvent and also depend on chemical composition of the solvent).
As plate develops you should see something like this:
- When solvent front pass ~2/3 or ~3/4 of the plate length remove plate from the solvent chamber and put it on the horizontal surface. Make sure you mark the solvent's front and middle of each stain you can identify on the plate. This is good time to take a picture of your TLC plate.
- Measure distances from the start line to the solvent front and to the middle of each spot. Write down results in your notebook.
Results and discussion.
First stage of our thin layer chromatography experiment we successfully separated black marker ink into three inks.
Best results were achieved on the corn starch plate using Mr Muscle glass cleaner as a solvent.
We found that black marker ink contains at least three colored inks: Red, Blue and Yellow. Yellow ink was the most mobile in the used chromatography system. We were not able to achieve complete separation of the pigments in our chromatography system and pigment spots were smeared along the plate and overlapping. It's good indication that our system was far from perfect though acceptable as chromatography for kids.
In second stage of our thin layer chromatography experiment we were going to check if pigments used in the black marker (A) and in yellow (B) and red (D) marker are the same. We also were going to find if green marker ink (C) is a simple ink or ink combination.
We expected to see yellow and red inks the same as yellow and red inks in the black marker.
The results are clearly show that in fact all inks used in the black marker are different from inks used in other markers! Green marker ink turned out to be a composition of blue and yellow inks. We were not able to achieve full separation of blue and yellow in our system. Yellow marker ink and yellow component of the green marker seem to be the same ink as their Rf are very similar.
More information on chromatography:
Thin layer chromatography - overall review. Explanation of principles of the method and some great illustrations of the results professionals can achieve with it.