Concerning TLC plates...
1. why should't I allow the solvent to reach the top of the plate?
(I assume it's the same as using paper like I did in gen chem but I'm not sure I know why it shouldn't be allowed to reach the top... what would happen?)
2. why sholdn't the spot sample placed on the plate be too large?
~my thought is that we would get mixed up in where the center of the spot is since it's too large or it could get mixed with the compound placed next to it if too large but I'm not sure.
If anyone wants to help me out it would be great..
~Thanks~
If the solvent is allowed to reach the top, then the separated spots continue moving to the top and eventually would recombine at the top and you would not have separated the spot into the different dompounds.
Larger sample spots may smear as the compounds separate.
Thanks Dr.Bob =)
1. When performing TLC (Thin Layer Chromatography), it is important not to let the solvent reach the top of the plate for a couple of reasons. The main reason is that the solvent reaching the top could potentially cause the spots to merge together, making it difficult to identify and analyze individual compounds. This happens because as the solvent ascends the plate, it can dissolve and carry the compounds with it, causing them to migrate further up and potentially overlap with other spots.
Additionally, allowing the solvent to reach the top can result in a loss of resolution. The separation of compounds on the TLC plate is based on their differing affinities for the stationary phase (typically a silica gel or alumina) and the mobile phase (solvent). The migration of compounds is driven by capillary action, and as the solvent travels a longer distance, there is a greater chance that compounds will have similar mobilities and overlap. This can make it challenging to accurately interpret and compare the relative positions of the spots.
2. It is important to avoid placing a large, concentrated spot on the TLC plate. As you mentioned, a large spot can indeed lead to issues with the analysis. One of the main problems is that a large spot may reduce resolution. The goal of TLC is to separate and visualize different compounds within a mixture, and this is achieved by comparing their relative positions on the plate. However, if the spot is too large, the compounds might spread out and blur, making it difficult to accurately determine their individual positions.
Furthermore, if the sample spot is too large, it can result in saturation of the stationary phase. TLC plates typically have a limited capacity to adsorb compounds, and if a large spot is applied, it may exceed this capacity. This can lead to distorted migration patterns and affect the accuracy of the analysis.
To obtain good results in TLC, it is recommended to use small, discreet sample spots. This helps to ensure separation and improve the clarity of the developed chromatogram.