Why do you need to remove the chromatogram before the solvent reaches the upper edge?
If it reaches the uppper edge, it "runs out of room" and the solute that has been separated below will begin to move up, also. If you leave it in the solvent long enough, all of the solutes will be together again at the top.
To understand why it is necessary to remove the chromatogram before the solvent reaches the upper edge, we need to understand the purpose and mechanics of chromatography.
Chromatography is a technique used in chemistry and biochemistry to separate and analyze mixtures into their individual components. It is based on the principle that different components of a mixture will move at different rates through a stationary phase (usually a solid or liquid) when subjected to a mobile phase (usually a liquid or gas).
In paper or thin-layer chromatography, a sample is spotted onto a stationary phase (paper or a solid plate coated with a thin layer of an inert material), and a solvent (the mobile phase) is allowed to move up the stationary phase through capillary action. As the solvent travels, it carries the individual components of the mixture with it, separating them according to their molecular properties, such as polarity or size.
Now, coming back to your question, it is important to remove the chromatogram before the solvent reaches the upper edge to ensure accurate and complete separation of the mixture components. If the chromatogram is not removed in a timely manner, the solvent will continue migrating upwards, potentially causing the individual components to merge together again or be smudged, compromising the separation.
Removing the chromatogram means taking it out of the solvent at a specific point in time, usually before the solvent front reaches the upper edge of the paper or the plate. This ensures that each component has had enough time to migrate and separate from the others, resulting in distinct spots on the chromatogram. Once the chromatogram is removed, it can be analyzed further by visualizing the spots or subjecting it to additional techniques like staining or spectrometry.
Overall, removing the chromatogram before the solvent reaches the upper edge is crucial to obtain accurate separation and analysis of the mixture components in chromatography.