What can go wrong in TLC chromatography?

What can go wrong in TLC chromatography?

The most common error in teaching TLC technique is solvent vapors inside the chamber not being equilibrated prior to use. The second most common mistake is the use of watch glass covers when beakers are used for TLC developing chambers.

How do you troubleshoot a TLC separation?

Troubleshooting Thin-Layer Chromatography

1. The cospot could help. If it looks like a snowman, your reaction is complete.
2. Try changing solvent systems.
3. Try staining with anisaldehyde. Compounds are different (bright) colors. Sometimes color differences are also visible with molybdenum stains.

What problem could arise if you made the compound spots too large on the TLC plate?

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.

How do I stop my TLC from streaking?

One way to remove the streaking is to add a few drops of ammonia (for amines) or formic acid (for carboxylic acids) to the eluting solvent.

What causes streaking in chromatography?

Streaking: If the sample spot is too concentrated, the substance will travel up the stationary phase as a streak rather than a single separated spot. In other words, the solvent can not handle the concentrated sample and in result, moves as much of the substance as it can up the stationary phase.

What happens when you spot too much material on a TLC plate?

Spotting the plate Allow the solvent to evaporate and spot at the same place again. This way you will get a concentrated and small spot. Try to avoid spotting too much material, because this will deteriorate the quality of the separation considerably (‘tailing’).

How do I select a solvent for TLC?

The choice of solvent or a mixture of solvents used in TLC is solely guided by two important factors : (a) the nature of the constituent to be separated i.e., whether it is polar or non-polar ; and (b) the nature of the process involved i.e., whether it is a case of ‘adsorption’ or ‘partition chromatography’.

What does 2 spots on a TLC plate mean?

Ideally, each compound in a mixture will produce a distinct spot so a sample with two compounds will give two different spots, and so on. An important property of any compound, is its Rf-value (retention factor). In simple terms, this value is an indication of how far up a TLC-plate a compound has wandered.

Why is Rf less than 1?

By definition, Rf values are always less than 1. An Rf value of 1 or too close to it means that the spot and the solvent front travel close together and is therefore unreliable. This happens when the eluting solvent is too polar for the sample.

At what height should you remove the TLC plate from the development tank?

Remove the plate when the solvent line is ∼0.5cm from the top. Immediately mark the solvent line with a pencil. Visualize if necessary.

Why is ammonia used in TLC?

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.

Why is TLC plate streaky?

Tailing / Streaks in TLC Plate: 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 and doing tailing. For overcome this problem, add a little triethylamine in mobile phase to solve this problem.

What are the common problems with thin layer chromatography (TLC)?

For this reason, it is important to be familiar with troubleshooting thin layer chromatography. Some of the common problems faced during TLC and their solutions are listed below: The thickness of the TLC slurry is uneven (usually seen when the TLC plate is prepared on a glass slide).

How do you do thin layer chromatography experiment?

Thin Layer Chromatography Experiment. The stationary phase that is applied to the plate is made to dry and stabilize. To apply sample spots, thin marks are made at the bottom of the plate with the help of a pencil. Apply sample solutions to the marked spots.

What is the line on a thin layer chromatography plate?

Usually, a thin layer chromatography plate is around 5–7 cm high, and a line is drawn around 0.5–1.0 cm from the bottom. That is the line in which you will spot your mixtures to separate. It is important that you spot the mixtures above the solvent level on your elution chamber!

What is the use of thin layer chromatography chamber?

Thin Layer Chromatography Chamber – Chamber is used to develop plates. It is responsible to keep a steady environment inside which will help in developing spots. Also, it prevents the solvent evaporation and keeps the entire process dust-free.