I tried to find a system to separate dimethyl-6,7-benzofuranone by using TLC but a big pigment appeared on the top of the TLC layer, Why?

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Madina Samenova

If a large pigment appeared on the top of the TLC (thin-layer chromatography) layer while attempting to separate dimethyl-6,7-benzofuranone, there could be several reasons for this:

Overloading the TLC plate: If you applied too much sample onto the TLC plate, it can lead to overloading. Overloading can cause the compounds to concentrate in a small area, leading to the formation of large spots or pigments that do not separate properly. Try applying a smaller amount of the sample to avoid overloading.

Insufficient solvent front migration: In TLC, the solvent front needs to migrate a sufficient distance up the plate for effective separation. If the migration distance is too short, the compounds may not separate adequately, leading to the formation of large spots or pigments. Ensure that the TLC plate is placed in a suitable developing chamber with enough solvent for proper migration.

Contaminants or impurities in the sample: If the dimethyl-6,7-benzofuranone sample contains impurities or contaminants, they may contribute to the formation of additional spots or pigments on the TLC plate. It's essential to ensure the purity of the sample before performing TLC.

Incorrect choice of TLC mobile phase: The selection of the appropriate mobile phase is crucial for effective separation in TLC. If the chosen mobile phase does not provide suitable resolution for dimethyl-6,7-benzofuranone, it can result in the appearance of pigments or poor separation. Consider trying different solvent systems or adjusting the polarity of the mobile phase to optimize the separation.

Chemical reactions or interactions: Certain compounds or impurities in the sample may undergo chemical reactions or interactions during the TLC process, leading to the formation of pigments or additional spots. This can occur if the sample or impurities are reactive or if the TLC conditions (e.g., temperature, humidity) favor such reactions.

To troubleshoot the issue, you can try the following:

Reduce the sample amount applied to the TLC plate.
Increase the migration distance by using a larger developing chamber or a more suitable solvent system.
Purify the dimethyl-6,7-benzofuranone sample to remove impurities.
Experiment with different mobile phases or adjust their compositions to improve separation.
Consider other chromatographic techniques, such as liquid column chromatography, if TLC fails to provide satisfactory separation.

Rana Hakimi

Madina Samenova thank you for your answer. Today I didn't add the sample to the TLC silica but the pigment on the layer's top is still present. I tried to change the mobile system, but the same result got.

Sylvester Darvin Sandhaanam

The pigment may be an impurity or contaminant present in your sample. It is possible that the dimethyl-6,7-benzofuranone you are attempting to separate contains a component that has a higher affinity for the stationary phase or has a stronger interaction with the TLC plate material. This can result in the formation of a concentrated pigment spot on the TLC plate.

Dominique Sagou

First you must know the polarity of this compound befor finding the système. For that you start with low polarity solvent for the best separation.

Chen Jingwen

Hi Rana,

The problem may be that sample is dissolved in the developing agent, or there are too many samples.