Over-large Spots: Spotting sizes of your sample should be not be larger than 1-2 mm in diameter. The component spots will never be larger than or smaller than your sample origin spot. If you have an over-large spot, this could cause overlapping of other component spots with similar (R_f) values on your TLC plate.

Correspondingly, why is a small spot of pigment needed on the TLC plate?

Use a different solvent and/or a different stationary phase, this means pigments which may have run together will separate out.

Similarly, why must the level of the solution in the developing chamber be below the spot on your TLC plate? It is extremely important that the solvent in the developing chamber be lower than the spotos on the plate, because the solvent must be drawn upward through the sample in order to draw the sample along with it. If the sample is dipped in to the solvent, the sample may simply dissolve in the developing solvent.

Likewise, people ask, why must the spot apply to TLC?

Why must the spot applied to a TLC plate be above the level of the developing solvent? The level of solvent or eluent must be below the level of the spots. Otherwise, the compounds will simply dissolve in the solvent and there will not be any spots left.

What does TLC tell you about purity?

Thin Layer Chromatography (TLC) is a separation technique requiring very little sample. It is primarily used to determine the purity of a compound. A pure solid will show only one spot on a developed TLC plate. In addition, tentative identification of the unknown compound can be made through TLC analysis.

Related Question Answers

What does a TLC plate tell you?

Thin layer chromatography, or TLC, is a method for analyzing mixtures by separating the compounds in the mixture. TLC can be used to help determine the number of components in a mixture, the identity of compounds, and the purity of a compound.

What happens if you apply too much compound 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. 3) What could happen if you spot too much of a compound on the TLC plate? Answer: The spot would show trailing. Answer: The spots would dissolve into the reservoir of eluting solvent.

Is silica polar or nonpolar?

Silica gel, the most commonly used stationary phase, has the empirical formula SiO2. However, at the surface of the silica gel particles, the dangling oxygen atoms are bound to protons. The presence of these hydroxyl groups renders the surface of silica gel highly polar.

What is the mobile phase in TLC?

The silica gel (or the alumina) is the stationary phase. The stationary phase for thin layer chromatography also often contains a substance which fluoresces in UV light – for reasons you will see later. The mobile phase is a suitable liquid solvent or mixture of solvents.

What is Rf value?

The Rf value is defined as the ratio of the distance moved by the solute (i.e. the dye or pigment under test) and the distance moved by the the solvent (known as the Solvent front) along the paper, where both distances are measured from the common Origin or Application Baseline, that is the point where the sample is

Why should you use pencil instead of pen to mark a TLC plate?

Do not use excessive forces when writing on a TLC plate as this will remove the stationary phase. It is important to use a pencil rather than a pen because inks commonly travel up the plate with the solvent. Using TLC pipettes, apply spots of analyte to the line. Make sure enough sample is spotted on the plate.

Is it possible to distinguish two spots that have the same Rf value?

5- Yes, it is possible to distinguish two spots that have the same Rf value but represent different compounds.

Why is it necessary to run TLC in a closed container?

It is necessary to run TLC in a closed container and have the interior saturated with the solvent vapor to ensure maximum resolution between components and to prevent solvent evaporating off. If the solvent evaporates off, the Rf value would be lower than the expected value.

How is RF value calculated?

With your ruler, measure the distance the solvent traveled, which is Df, and measure the distance the test solution traveled, which is Ds. Calculate the retention factor using this equation: RF = Ds/Df. Simply divide the distance the solution traveled by the distance the solvent traveled.

What do TLC plates tell you?

Thin layer chromatography, or TLC, is a method for analyzing mixtures by separating the compounds in the mixture. TLC can be used to help determine the number of components in a mixture, the identity of compounds, and the purity of a compound.

What is TLC chamber?

Thin-layer chromatography (TLC) is a chromatography technique used to separate non-volatile mixtures. Thin-layer chromatography is performed on a sheet of glass, plastic, or aluminium foil, which is coated with a thin layer of adsorbent material, usually silica gel, aluminium oxide (alumina), or cellulose.

What happens if the solvent front reaches the top of the plate?

If the plate enters the solvent at an angle, it will cause a slanted solvent front line which may result in poor separation and uneven alignment of the spots. When the solvent front is about 0.5 to 1 cm from reaching the top, it's time to stop the elution. Do not allow the solvent front to reach the top of the plate.

Why is TLC important?

Thin-layer chromatography (TLC) is a very commonly used technique in synthetic chemistry for identifying compounds, determining their purity and following the progress of a reaction. It also permits the optimization of the solvent system for a given separation problem.

Why should a TLC plate be removed?

TLC. Allow the solvent to climb up the TLC plate, and remove the plate when the solvent nearly reaches the top. Quickly, before the solvent evaporates, mark the solvent front.

How does polarity affect RF value?

In general, the adsorptivity of compounds increases with increased polarity (i.e. the more polar the compound then the stronger it binds to the adsorbent). 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).

How do you make a TLC plate?

TLC Slurry preparation for soft layer coating:
  1. Silica Gel and small amount of calcium sulfate (gypsum) is mixed with water.
  2. This mixture is spread as a thick slurry on a clean glass plate.
  3. The resultant plate is dried and activated by heating in an oven for thirty minutes at 110°C.

What does Rf value tell you about purity?

However, because Rf values are relative, not absolute, some compounds may have very similar Rf values. A mixed melting point measurement is needed to unambiguously identify the unknown compound. It is primarily used to determine the purity of a compound. A pure solid will show only one spot on a developed TLC plate.

Why do we use TLC?

Thin layer chromatography, or TLC, is a method for analyzing mixtures by separating the compounds in the mixture. TLC can be used to help determine the number of components in a mixture, the identity of compounds, and the purity of a compound.