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CHROMATOGRAPHY AT HOME

 

For the separation of various mixtures for the analysis and allocation of separate mixtures of substances in laboratories often use chromatography: this is one of the best methods of separation and analysis of mixtures. Chromatography is used in industry, when you need to clean up and share similar substances - organic and inorganic, from lanthanides to amino acids. Its essence is that the individual components of the mixture (liquid or gas) different withheld substance adsorbent capable of selectively absorb certain chemical compounds.

Modern gas and liquid chromatographs - complex devices with automatic control, often with micro-computer, which plans the course of the study and provides the results. Of course, this is not available for home lab, nor for the mug. However, began this method of analysis with simple tricks that are affordable and a budding chemist.

Let's start with paper chromatography. Analytical chemists use special chromatographic paper, but for our experiments a suitable conventional filter paper or blotting paper. Take a square piece of paper and in the middle of the drip test solution containing a mixture of colored substances. This can be alcoholate of any medications, such as Valerian or calendula, or you have prepared extract of chlorophyll (see "Extraction"), or a mixture of dyes, composed specially for this experience. On paper formed the spot. In the center of his place a few drops of solvent in the above examples, the solvent should serve alcohol, and Cologne it cannot be replaced - it contains substances that can pervert the course of experience. Instead of ethyl alcohol can be rented isopropyl - called IPS it is sold in hardware stores as a means for washing Windows.

So, you have dripped a few drops of solvent, and he seemed to wick, moving between the paper fibers, carries colored substances from the spot in all directions. Depending on the nature of the substance and its molecular weight experience goes faster or slower, but sooner or later on the sheet is several rings of different colors. How many rings is dependent on how many chemicals were in the analyzed mixture.

Experience with chlorophyll such rings will be two: yellow and grey.

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

Rabbanite starch in a small amount of alcohol (again, you can get isopropyl alcohol), pour the mixture on the glass and allow the solvent to evaporate. When the plate becomes dry, in its center, as paper, put a drop of the studied mixtures; of course, it should be painted, otherwise the division will be hard to notice. The object of the experiment find themselves. In addition to what was already called, are painted juices, ink, gouache paints, and more.

Allow the stain to dry and drip one or two drops of solvent. If rasplivaetsa spot will leave a sorbent-starch is not one, but two or more colored rings, this will indicate that you no longer had to deal with an individual substance, and with the mixture.

Version of experience with thin-layer chromatography: a plate with a test substance inclined put into a glass, the bottom of which is poured quite a bit of solvent to wet a little starch. The solvent (alcohol) will rise starch, reaches drops of the mixture will go even higher, and the mixture will be divided into components: they held different adsorbent - starch.

Not less common in laboratory column chromatography, in which a mixture is separated into columns Packed with the sorbent. Such a method, perhaps, to be more precise, but it requires patience, because the solution in the column is moving slowly.

The chromatographic column will serve a glass tube with a diameter of about 1 cm and a length of about 20 cm . Close wool its lower end and stir in the starch or powdered sugar a little more than half. From top to pour in the receiver solution of the analyte, preferably not too high concentrations. When the solution-impregnated with starch or powder in the column about half its height, pour 3-4 ml of pure solvent. Mix up the height of the column will be clearly visible painted rings. They will be as much as substances included in the composition of the studied mixture. This experience is good, in particular, to extract chlorophyll, if the solvent is taken pure gasoline (no car, and benzene).

O. Holguín. "Experiments without explosions"
M., "Chemistry", 1986

 

Your comments:

Lily
2013-09-12 15:53:16
I want to find experiments at home
sandy
2012-12-16 17:23:23
it is very difficult
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