Sometimes a developed TLC plate may show streaks, crescents or strangely shaped spots, and these are all indicative of different problems. Streaks. There are several reasons why you may see a streak up the plate. Firstly, you may have overloaded the plate, and if you reduce the amound of material spotted on the baseline, you will increase the resolution on your plate.
Why are there streaks on my TLC plate?
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.
What are some common problems encountered in TLC?
Examples of common problems encountered in TLC: The compound runs as a streak rather than a spot: The sample was overloaded. The sample runs as a smear or a upward crescent: Compounds which possess strongly acidic or basic groups (amines or carboxylic acids) sometimes show up on a TLC plate with this behavior.
How do I protect my skin when using a TLC plate?
Protect your skin by wearing gloves. If the TLC plate runs samples which are too concentrated, the spots will be streaked and/or run together. If this happens, you will have to start over with a more dilute sample to spot and run on a TLC plate. Here's what overloaded plates look like compared to well-spotted plates.
What is the cause of tailing in 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.
Why does my TLC plate curve?
The reason for this is that the solvent doesn't run perfectly level up the plate, this is most evident at the edges of the plate. If you re-run your TLC plates with a shorter band, you should see a decrease in the curving effect that you're observing.
How is TLC run?
TLC is most usually ran by applying a small spot of the sample to the plate, and allowing it to run up. Analytically, this gives the greatest resolution, and as such for things such as monitoring reactions or identifying components in column chromatography fractions, spots are the most widely used.
How far should a PLC plate be from the edge?
When applying bands to the PLC plate, it's crucial to ensure that the band doesn't get too close to the edges (as it has in the images you've uploaded), as a rule of thumb, at least 1/2 cm from each side should be left clean.
What is tailing in TLC?
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.
Why does tailing occur in a sample?
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.
Why does silica gel have tailing?
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.
How to solve for tailing?
Amine gives tailing. Solve it by adding few drops of triethylamine in the solvent mixture.
Why does Teledyne tail on silica gel?
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.
What happens if you run a solvent up a plate?
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.
What compound gives tailing?
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.
What is uneven thickness of TLC?
The thickness of the TLC slurry is uneven (usually seen when the TLC plate is prepared on a glass slide). The plate touches the sides of the container/chamber/filter paper.
Why is there no compound in the sample?
There is no compound in the sample due to experimental failure. The level of the solvent system is too high. If the level of the solvent system in the chamber is above the spot when the plate is inserted, the compound from the spot will dissolve in the solvent instead of migrating up the plate.
Can you perform TLC for any sample?
As has been noted, you might face several problems while performing TLC for any given sample, but with repetition you will move towards perfecting your TLC experiment. Best luck with your TLC.
Is TLC easy to do?
The whole TLC technique sounds easy to do, but it can be difficult and tricky during interpretation or give unexpected results, especially when working with biomolecules. For this reason, it is important to be familiar with troubleshooting thin layer chromatography.
Why can't you see spots after a TLC plate is developed?
If the solvent level in the developing jar is deeper than the origin (spotting line) of the TLC plate, the solvent will dissolve the compounds into the solvent reservoir instead of allowing them to move up the plate by capillary action. Thus, you will not see spots after the plate is developed.
Why does a compound run as a streak?
The compound runs as a streak rather than a spot: The sample was overloaded. Run the TLC again after diluting your sample. Or, your sample might just contain many components, creating many spots which run together and appear as a streak. Perhaps, the experiment did not go as well as expected.
What is the purpose of TLC chromatography?
Since TLC is a much faster procedure than column chromatography, TLC is often used to determine the best solvent system for column chromatography.
Why is the solvent front crooked?
The plate solvent front runs crookedly: Either the adsorbent has flaked off the sides of the plate or the sides of the plate are touching the sides of the container (or the paper used to saturate the container) as the plate develops . Crooked plates make it harder to measure R f values accurately.
How to make a TLC chamber?
Step 1: Prepare the developing container. The developing container for TLC can be a specially designed chamber, a jar with a lid, or a beaker with a watch glass on the top (the latter is used in the undergrad labs at CU). Pour solvent into the chamber to a depth of just less than 0.5 cm.
What is a TLC plate?
A TLC plate is a sheet of glass, metal, or plastic which is coated with a thin layer of a solid adsorbent (usually silica or alumina). A small amount of the mixture to be analyzed is spotted near the bottom of this plate. The TLC plate is then placed in a shallow pool of a solvent in a developing chamber so that only the very bottom ...
How does a TLC plate work?
The TLC plate is then placed in a shallow pool of a solvent in a developing chamber so that only the very bottom of the plate is in the liquid. This liquid, or the eluent, is the mobile phase, and it slowly rises up the TLC plate by capillary action.
Popular Answers (1)
Compounds which is basic in nature are often tailing on silica coated TLC plate because silica is acidic in nature so they interact with one another, resulting in tailing. To overcome this problem, add a little triethylamine in mobile phase https://madhavuniversity.edu.in/basics-of-layer-chromatography.html
All Answers (3)
Spot smearing can be caused by many things. First, 2 generic basics: Make sure, that the TLC chamber is sufficiently saturated with vapor from your mobile phase, so let the chamber stand filled with the mobile phase for a while before starting the TLC.
Why does pyridine spread out on TLC?
The pyridine spreading out on your TLC is probably related to its volatility. You will see the same effect with toluene. The BP is high enough to evaporate slowly during drying of the plate, but low enough to diffuse rapidly during its further drying.
What to add to TLC?
So the general response I've been getting is that if basic/acidic compounds are being run on the TLC, add some base (NEt3/ammonia) or acid (acetic acid) respectively .
How long should I dry TLC plates?
I also dry my TLC plates on the vacuum line for at least 5-10 minutes, especially if the sample contains water. I'll sometimes use a heat gun to heat the plate for a few seconds in the fumehood, but not for samples in water.
Is TLC similar to silica?
Be aware that a TLC is pretty much comparable to a silica column and that if the compound tails on TLC it will probably tail on your column as well. Modifiers are great to prevent this, even at larger scale.
