Chromatography at home. Fun chemistry experience at home

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Chromatography at home. Chemical experiments

Entertaining experiments in chemistry

Entertaining experiences at home / Chemistry experiments for children

To separate various mixtures, to analyze and isolate individual substances from mixtures, chromatography is very often used in laboratories: this is one of the best methods for separating and analyzing mixtures. Chromatography is also used in industry when it is necessary to purify and separate similar substances - organic and inorganic, from lanthanides to amino acids. Its essence is that the individual components of the mixture (liquid or gas) are differently retained by the adsorbent substance, which is capable of selectively absorbing certain chemical compounds.

Modern gas and liquid chromatographs are complex devices with automatic control, often with a microcomputer that plans the course of the study and produces ready-made results. Of course, this is not available either for the home laboratory or for the circle. However, this method of analysis began with simple techniques that are accessible to a novice chemist.

Let's start with paper chromatography. Analytical chemists use special chromatographic paper, but ordinary filter paper, or even a blotting paper, will do for our experiments. Take a square piece of paper and drop the test solution containing a mixture of colored substances into the middle. This may be an alcohol tincture of a medicine, such as valerian or calendula. or a chlorophyll extract prepared by you (see chapter "Extraction"), or a mixture of dyes, compiled specifically for this experiment. A stain forms on the paper. Drop a few drops of solvent into its center: in the above examples, alcohol should serve as a solvent, and you cannot replace it with cologne - it contains substances that can distort the course experience Instead of ethyl alcohol, you can take isopropyl - under the name IPA it is sold in hardware stores as a window cleaner.

Chromatography at home

So, you dripped a few drops of solvent, and it, as if along a wick, moving between paper fibers, spreads the colored substances from the stain in all directions. Depending on the nature of the substance and its molecular weight, the experiment goes faster or slower, but sooner or later there are several rings of different colors on the sheet. How many rings - depends on how many substances were in the analyzed mixture.

In the experiment with chlorophyll, there will be two such rings: yellow and gray.

You can come up with many variations of this experience using different mixtures and suitable solvents. And even more accurate results can be obtained if, instead of paper, a thin layer of sorbent is used, applied, for example, to glass. This version of the method is called thin-layer chromatography, and starch can serve as a sorbent substance in the simplest case.

Dissolve the starch in a small amount of alcohol (again, you can use isopropyl alcohol), pour the mixture onto the glass and let the solvent evaporate. When the plate becomes dry, drop one drop of the test mixture into its center, as well as onto paper; of course, it must be colored, otherwise the separation will be difficult to notice. Choose the object for the experiment yourself. In addition to what has already been mentioned, colored juices, inks, gouache paints and much more are suitable.

Let the stain dry and apply one or two drops of solvent. If a spreading spot leaves not one, but two or more colored rings on the starch sorbent, this will indicate that you were dealing not with an individual substance, but with a mixture.

A variant of the experiment with thin-layer chromatography: a plate with the test substance is placed obliquely in a glass, on the bottom of which quite a bit of solvent is poured - so that it wets a little starch. The solvent (alcohol) will rise through the starch, reach a drop of the mixture, move even higher, and the mixture will be divided into components: they are held differently by the adsorbent - starch.

No less common in the laboratory is column chromatography, in which mixtures are separated on columns filled with a sorbent. This method is perhaps even more accurate, but it requires patience because the solution in the column moves slowly.

A glass tube with a diameter of about 1 cm and a length of about 20 cm will serve as a chromatographic column. Cover its lower end with cotton and add starch or powdered sugar a little more than half. From above, pour a solution of the test substance into the tube, preferably not too high a concentration. When the solution has soaked the starch or powder in the column to about half its height, pour in 3-4 ml of pure solvent. The mixture will accelerate along the height of the column, the colored rings will become clearly visible. There will be as many of them as there are substances in the mixture under study. This experiment works well, in particular, with an extract of chlorophyll, if pure gasoline is taken as a solvent (not automobile, but solvent gasoline).

Author: Olgin O.M.

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