It’s used to test for the presence of various materials, to monitor the rate and progress of a reaction or to determine the purity of a product. Filter paper impregnated with solvent is usually used to saturate the development chamber’s air with solvent vapor so the stationary phase doesn’t dry during the process.

When the solvent has reached the top of the plate, the plate is removed from the developing chamber, dried, and the separated components of the mixture are visualized. If the compounds are colored, visualization is straightforward. Usually the compounds are not colored, so a UV lamp is used to visualize the plates.

Question: How Long Should You Run A TLC Plate For? Until The Solvent Front Is About Half Way Up. Until The Solvent Front Is At The Top Of The Plate. 2 Minutes.

one spot

More than 1 compound can be separated on a TLC plate as long as the mobile phase is preferred for each compound. TLC plates do not have long stationary phases. Therefore, the length of separation is limited compared to other chromatographic techniques.

In thin-layer chromatography, the retention factor (Rf) is used to compare and help identify compounds. The Rf value of a compound is equal to the distance traveled by the compound divided by the distance traveled by the solvent front (both measured from the origin).

The stronger a compound is bound to the adsorbent , the slower it moves up the TLC plate. Non-polar compounds move up the plate most rapidly (higher Rf value), whereas polar substances travel up the TLC plate slowly or not at all (lower Rf value).

Questions from the experiment:Why are the spots the same for both the right and left lanes? This is because the reaction has only just begun and a complete reaction has not been yet completed.

2) What could happen if you used ink to draw in your base line and letters on the TLC plate? Answer: The ink might travel with the eluting solvent and separate into its component pigments, giving you a lot of extraneous spots.

The cospot is important for reactions where reactant and product have similar Rfs. Also, in some cases the reaction mixture affects the appearance of the reactant during chromatography. The reactant can appear to be gone, but in actuality just looks different on TLC under the reaction conditions.

By observing the appearance of a product or the disappearance of a reactant, it can also be used to monitor the progress of a reaction. TLC is a sensitive technique – microgram (0.000001 g) quantities can be analyzed by TLC – and it takes little time for an analysis (about 5-10 minutes).

The principle of TLC is the distribution of a compound between a solid fixed phase (the thin layer) applied to a glass or plastic plate and a liquid mobile phase (eluting solvent) that is moving over the solid phase.

The rate can be determined by measuring:

1. changes in the concentration of the reactants or products.
2. changes in the mass of the reactants or products.
3. changes in the volume of the reactants or products.

You can follow the progress of the reaction by periodic analysis using simple TLC or GC, and can stay with the reaction until it is complete. All the starting material is consumed, and one new product is formed cleanly (aka “spot to spot”).

Reaction rate is calculated using the formula rate = Δ[C]/Δt, where Δ[C] is the change in product concentration during time period Δt. The rate of reaction can be observed by watching the disappearance of a reactant or the appearance of a product over time.

WHAT SORT OF WAYS CAN WE MEASURE THE SPEED OF A CHEMICAL REACTION? The phrase ‘rate of reaction’ means ‘how fast or how slow is the reaction’ or ‘the speed of the reaction’. It can be measured as the ‘rate of formation of product’ (e.g. collecting a gaseous product in a syringe) or the ‘rate of removal of reactant’.

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