Why is propanol ammonia a better separator of red leaf extract in thin layer chromatography that propanol water?
There are a couple of possible reasons.
I don't know what red leaf extract is?? Is it red tea extract?
I take it that the stationary phase of the TLC is silica gel? It is quite likely that the extact contains a number of nitrogen containing compounds, such as alkaloids (it will if it is tea). These compounds are quite polar and tend to stick well to silica, resulting in blobs that smear up the TLC plate with little separation or do not move at all.
By adding ammonia to the mobile phase this makes the silica less effective at holding on to the alkaloids as in effect the acid silica gel has been neutralised. This tends to give better separation as you get spots that move rather than getting a smear up the plate.
Often the amount of ammonia needed is a matter of trial and error. Some chemists also use other amines such as propylamine, but again the choice and how much is a matter of trial and error.
You can also get TLC plates that are coated with alumina, which is already basic.
(I used to have to make my own TLC plates and got quite adept at adding ammonia to the water slurry that the plates were made from - but it meant I had a lot of smelly TLC plates drying!)
To understand why propanol ammonia is a better separator of red leaf extract in thin layer chromatography (TLC) compared to propanol water, we need to consider the principles of chromatography and the properties of the solvents involved.
Thin layer chromatography is a technique used to separate and analyze different components of a mixture based on their affinity to the stationary phase (usually a solid support) and the mobile phase (usually a liquid solvent). In TLC, a small amount of the mixture is applied as a spot onto the stationary phase, and as the mobile phase moves up the plate through capillary action, the components of the mixture separate into distinct bands.
The choice of solvent for the mobile phase is crucial in TLC because it affects the separation and migration of the components. Solvents differ in their polarity, which is determined by their chemical structure and functional groups. Ideally, the mobile phase solvent should have a polarity that is compatible with the sample being analyzed, allowing for good separation.
In the case of separating red leaf extract, the choice of solvent can be guided by the polarity of the compounds present in the extract. Propanol ammonia, a mixture of propanol (a polar solvent) and ammonia (a basic compound), is often preferred over propanol water because of its superior solvent properties when it comes to polar compounds.
Ammonia acts as a base and can interact with acidic components present in the red leaf extract. This interaction can lead to the formation of ionic species or hydrogen bonding, enhancing their separation during TLC. Additionally, ammonia can also act as a pH adjuster, maintaining a favorable pH for the separation of certain compounds.
Propanol, on the other hand, is a polar solvent that can dissolve a wide range of compounds, including polar and nonpolar ones. It is often selected as a mobile phase solvent in TLC due to its ability to provide good separation and migration for a variety of compounds.
By combining propanol and ammonia together, a synergistic effect is achieved, as the mixture benefits from the solvent properties of both components. This allows for better resolution and separation of the different components present in the red leaf extract during TLC.
In contrast, propanol water, which lacks the basicity of ammonia, may not provide sufficient interactions with acidic components and could result in poorer separation. The presence of water in the organic solvent mixture can also affect the polarity and overall solvent strength, potentially compromising the separation efficiency.
In summary, propanol ammonia is a better separator of red leaf extract in thin layer chromatography compared to propanol water due to the synergistic effect of propanol's solvent properties and ammonia's basicity, which allows for better interaction with the components of the extract and improved separation on the TLC plate.