There's a couple of things that may be going on-

1) Make sure the chamber is saturated with vapor. An unsaturated chamber causes solvent to be evaporated from the TLC plate. One colvent may be evaporated faster than the other leading to a poorly shaped solvent front, and also giving irreproducible chromatography. A course paper towel or filter paper sheet placed in the chamber with the solvents helps to saturate the chamber. Some solvents, such as those containing water or ammonia as part of the mobile phase, may take some time to become saturated. Do not take much time to place the plate in the chamber of the vapor is lost.

2) Make sure the edge of the plate isn't touching anything (like the paper mentioned above or the side of the chamber). Some people use a beaker covered by a watchglass as a chamber; the edge of the plate may touch the side of the beaker. The beaker spout may also let vapor out of the chamber

Cut the TLC plates straight line .Cut little bottom corners of theTLC plate.Spot the compounds dilute in TLC plate and dry TLC plate before running. When you place your TLC plate into a TLC chamber, the level of the TLC solution must be below your TLC spots.

Take some precautions:

1. TLC plate should be flattened

2. Apply the appropriate quanity of sample (depends on silica plate thickness) and dry the spot in air

3. Place the TLC chamber at flat surface and put the strip in it in the manner that the spot should be just above the solvent line.

There's a couple of things that may be going on-

1) Make sure the chamber is saturated with vapor. An unsaturated chamber causes solvent to be evaporated from the TLC plate. One colvent may be evaporated faster than the other leading to a poorly shaped solvent front, and also giving irreproducible chromatography. A course paper towel or filter paper sheet placed in the chamber with the solvents helps to saturate the chamber. Some solvents, such as those containing water or ammonia as part of the mobile phase, may take some time to become saturated. Do not take much time to place the plate in the chamber of the vapor is lost.

2) Make sure the edge of the plate isn't touching anything (like the paper mentioned above or the side of the chamber). Some people use a beaker covered by a watchglass as a chamber; the edge of the plate may touch the side of the beaker. The beaker spout may also let vapor out of the chamber

@ Mr. Jack silver: agreed with your answer........

Just cut the corners of TLC and remove the seeding solvent with help of a heat gun i order to avoid diffusion over the TLC plate, it’s really important to have a small seeding line. In addition try to saturate the TLC chamber following the previous suggestion of other colleagues.

Mr. Jack silver: agreed with your answer........

I want to add some points in it.

1. TLC plate must be activated before application of sample.

2. Angle of placing plate in chamber is also important.

3. Follow same environmental condition through out your experiments

Thanks everyone for your valuable suggestions

In addition to previous suggestions: make sure you do not touch the layer on the plate with anything at any time--handle it only by the edges--and/or the plate is in good condition (e.g. we got the same problem developing old silica gel plates).

Mobile phase composition changes while running the TLC plate. Miscibility of mobile phase solvents give rise to improper running of TLC. Also proper mixing of solvent is required. i.e. For mixture of Ammonia, water, Methanol and Chloroform, Mix first ammonia in water then this mixture in methanol and then methanol mixture slowly in Chloroform.

I;ve always had problems with cutting Al-silica plates with scissors (cutting the corners doesn't always work), so I use a sharp razor - just score the Al side of the plate with razor and strightedge and carefully bend the plate along the score until it breaks.

by the description you give, on top of above suggestions may be your silica plates are defective, i.e., if only after one quarter of solvent development and not from the start you observe the abnormality, may be your silica plates have been not properly stored. Try with other brand new ones or try to “dry” or activate the ones you have been using. Good work.

To check whether the plates have a problem is the best thing because procedural mistakes can be corrected after following the above suggestions. A small experiment will fix your problem.

Make a new TLC plate using silica gel-G slurry on a glass plate. Now saturate a chamber properly and completely using filter paper alongside the walls of the chamber. Once saturated fully, leave it for another 15 mins, then remove filter paper and cover it with a glass plate using paraffin wax on the top of the chamber walls which makes it airtight. If you have a covered chamber already, this is not required.

Take your aluminium silica sheet. Cut it properly and in the same dimensions as the glass TLC plate prepared by you. Activate both the plates together in a hot air oven for 30 mins at 110 C. Apply your spots on both the plates.

Keep them together in the fully saturated chamber on opposite sides. Observe the development in both of them. If the silica plate still behaves the same and the glass plate develops correctly, then your silica plates have a problem. If both behave the same way, then procedure/ solvent system has a problem. At least you now can have an idea about the root cause of the problem.

Regards

Be sure the edges of the plates are smooth and cut straight .

Preparation of Mobile phase is a key parameter in this case. Mix the solvents by stirring with magnet at moderate speed and sonicate this mobile phase for suitable time.

Secondly TLC plate needs to be activated at 100 Degree centigrade before spotting.