Chromatography is a physicochemical technique for separation of mixtures, based on the differential migration of substances over a fixed phase, called the stationary phase.
In this method, there is always a substance capable of fixing the substance being separated on its surface, and a fluid solvent that “drags” the material to be isolated.
One of the first processes used was paper chromatography. The substances to be separated usually interact with the cellulose in the paper, and because of their different constitutions, some migrate faster and others less quickly.
To visualize this phenomenon, a simple experiment can be done in the laboratory, classroom, or even at home. You will need the following materials:
- Filter paper (coffee strainer);
- different colored porous tip pens;
- A support (may be some straight container);
- Alcohol;
- Dropper.
Do the following: Cut the filter paper to the desired shape – just make sure it's straight and flat. Place it on top of a support so that it is very firm. Then make a circle with dots of different colors of felt-tip pens. Drop alcohol into the center of the circle and note what happened. Continue dripping alcohol until you get the desired effect.
It was observed that when the ethyl alcohol solvent was added, the colors began to spread and in some cases we noticed the presence of more than one dye in the pen ink composition.
This is because some dyes interact more strongly with the solvent (they are moving, spreading across the paper) and others interact better with the paper (which is stationary).
This procedure can also be done with some old shirt that you want to dye and make a different effect as shown in the figure below.
By Jennifer Fogaça
Graduated in Chemistry
Brazil School Team
Source: Brazil School - https://brasilescola.uol.com.br/educacao/experimento-cromatografia-papel.htm
