There could be several reasons for tailing. Basic compounds often tail on silica gel (I didn't see what type of TLC plates you are using) because they interact with the slightly acidic silica. Adding a little tri-ethyl amine often solves this issue. The use of ammonia also sometimes helps. For acidic compounds, a little formic or acetic acid sometimes helps to make tighter spots.

If the sample is heavily applied, there could be solubility issues. The solvent running up the plate can only carry a maximum amount of compound; the remainder gets picked up by solvent running up the plate a little later, causing a streaked spot.

Another possibility is that the compound is decomposing, creating streaks on the plate. The use of another TLC plate such as alumina, diol, or C18 may avoid this problem as they are often less reactive than silica.

Also make sure the TLC plate chamber is properly saturated with vapor.

Use a mixture of polar and non-polar solvents (e. g. cyclohexane and propanol, etc.), their kind and ratio you must search experimentally.

If you would like to find out whether your compound is decomposing on the TLC, there is an easy way. Just do a 2D TLC. If the compound is decomposing, than you will get a tailing in both directions.

If your compound possesses strong hydrogen bonding functional groups then I find that adding a little acetic acid or triethylamine helps (depending on compound tolerance). Though I agree with Jack, most common problem with tailing is overloading the TLC. In this instance tip out an NMR sample then refill with chloroform (or something along those lines), this will dilute the residual amount of compound in the tube to a nice TLC visualization level.

Mostly s its because of samples concentration. Not only the concentrated liquid could cause tailing but also being nitrogen in your sample could cause it too.

Try a different solvent system: Hexane/EtOAc or Benzene/EtOAc. It would also help if you don't overload the plate by spotting it with too much material.

TLC  is  tailing in TLC may be due to incorrect solvent system or no activation of the silica gel which must be heated to 110 deg. for activation before use OR improper spreading of silica gel slurry on the glass plate.

Practically I have encountered similar problem while dealing with heavily functionalized molecules and majority in case with natural products. The above suggested methods of triethylamine and formic acid works very well, one more thing which can be performed is avoiding the extensive hydrogen bond formation with your compound as well, this can be done by replacing the solvents like ethyl acetate/methanol with chloroform/dichloromethane in hexane. changing the solvent system worked as a charm for me, it might help you too. Good luck

I tried both Acetic acid for acidic compound tailing, and Triethyl amine for basic compounds tailing both TEA, and AcOH prevent the tailing

I came across the same problem, one of the reasons could be overloading the sample on the TLC plate. all'd suggest you dilute the sample before loading it on the TLC plate

Amine gives tailing. Solve it by adding few drops of triethylamine in the solvent mixture.

Tailing in TLC - is due to incorrect solvent system i.e.moving phase. The TLC of liquid may cause tailing.

Could you add few drops of ammonia solution or DMF in moving phase and check TLC.

Or add few drops of triethylamine. The tailing is also due to interaction of the basic secondary metabolites with acidic silinol groups of the silica gel packing material if the plates used were silica plates.

Tailing in TLC; is due to the incorrect solvent system moving phase. Some of the compounds such as amine gives tailing. You can solve it by adding a few drops of triethylamine in the solvent mixture.

Tailing or a broad spot is seen when the solvent phase system is not appropriate for the product formed. Generally polar crude product give such type of tailing. Please put very little spot of crude product on TLC plate and choose solvent phase mix wisely.

there are several reasons for streaks on TLC plate. Compound which is basic or acidic for this to overcome this problem by adding triethylamine in mobile phase in case of basic, by adding acetic or formic acid in mobile phase in case of acidic, or sometimes we load max amount of compound on TLC, so we should dilute the sample, or decomposition of compound in this case use less reactive TLC plates such as alumina coated, diol coated and C18 coated TLC plates