Why do you use a pencil rather than a pen to mark the spotting line on 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.
Why is it important to use only a pencil to mark the starting line of the chromatogram?
Answer and Explanation: In paper chromatography, the starting line must be drawn with the help of pencil because the pencil lead does not dissolve in solvent, thus it will not affect the separation. The spots of the compounds are separated correctly.
Why is it necessary to use a pencil instead of a pen or a marker?
Because pen ink will undergo the chromatography process and mess up your results. Pencil contains only graphite, while pen ink contains a variety of compounds, which would become separated by the process.
Why do you have to use a pencil and not a pen when marking the baseline and any labels on the chromatography paper?
You can’t use a pen because the ink will travel up the TLC plate with the TLC solvent, just like your chemical samples do. You can only spot/label/mark TLC plates using a pencil. The graphite in a pencil will not run up the plate!
Why can’t the solvent touch the pencil line?
If your start line is inside the solvent or equal to level of solvent it can cause error. The solvent gives extra energy to pull up the sample and the sample will also dissolve in the solvent. That’s why as precautionary measure start line should stay above the solvent in chromatography!
What happens if the spot line and positions are marked on the plate with a ballpoint pen when preparing a TLC plate for development?
What happens if the spot line and positions are marked on the plate with a ballpoint pen when preparing a TLC plate for development? Ballpoint pen ink consists of organic compounds that will move with the development solvent and cause additional spots to appear on the plate.
What happens if the spots are made too large when preparing a TLC plate for development?
What happens if spots are made too large when preparing a TLC plate for development? Why must the spots be above the level of development solvent in chamber? They will dissolve in the development solvent if they were submerged.
How long should you run a TLC plate for?
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.
What would happen if you spotted too much sample 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.
Does a higher Rf value mean more polar?
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).
Why silica gel is used in TLC?
Silica gel is by far the most widely used adsorbent and remains the dominant stationary phase for TLC. The surface of silica gel with the highest concentration of geminal and associated silanols is favored most for the chromatography of basic compounds because these silanols are less acidic.
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.
What is TLC used for?
TLC is a chromatography technique used to separate non-volatile mixtures. Thin-layer chromatography can be used to monitor the progress of a reaction, identify compounds present in a given mixture, and determine the purity of a substance.
What are the advantages of TLC?
Advantages of TLC include rapid analysis time because many samples can be analyzed simultaneously, low solvent usage on a per‐sample basis, a high degree of accuracy and precision for instrumental TLC, and sensitivity in the nanogram or picogram range.
Why do we use TLC?
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.
What is TLC principle?
The mobile phase is a solvent chosen according to the properties of the components in the mixture. 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.
Why the TLC chamber has to be covered while TLC plate is being developed?
This has to do with the vapor pressure of the solvent. If there’s no cap, the pressure of the TLC chamber is too low and it won’t travel up the TLC plate. So always use a lid.
What is TLC plate?
Thin-layer chromatography (TLC) is a chromatography technique used to separate non-volatile mixtures. After the sample has been applied on the plate, a solvent or solvent mixture (known as the mobile phase) is drawn up the plate via capillary action.
What does TLC mean sexually?
Tender Love And Care
How can TLC be used to identify a compound?
A quick TLC analysis can be used to identify whether or not an unknown compound is the same as another known compound. If we find that the two spots have the same Rf-values, and the third spot only shows one spot, the two compounds are identical. The second common way to use a TLC- plate, is to monitor a reaction.
How do I get a TLC plate?
TLC Slurry preparation for soft layer coating: Silica Gel and small amount of calcium sulfate (gypsum) is mixed with water. This mixture is spread as a thick slurry on a clean glass plate. The resultant plate is dried and activated by heating in an oven for thirty minutes at 110°C.
Is TLC plate transferable?
TLC license plates are non-transferable but, like medallions, are considered an asset to a company.
Why do we use filter paper in TLC?
The filter paper should be as tall as the beaker. The purpose of the paper is to saturate the air in the beaker with the solvent vapours. If the air is not saturated with solvent, the solvent that is rising up the plate will evaporate in an attempt to saturate the air.
What causes streaking on TLC plates?
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 does the RF value tell you in TLC?
The Rf value (for TLC) is simply the (migration distance of substance)/(migration distance of solvent front). The Rf value is often used, along with other evidence, to help identify a compound when compared with a known standard.
Which solvent system gave the best results?
Which solvent system gave the best results? The 75% hexane and 25% ethyl acetate gave the best results.
How do you calculate RF?
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).
How do you choose the best solvent for chromatography?
For most separations, the solvent should be less polar than the compounds. The compounds must also be soluble in the solvent so they are not permanently adsorbed.
Do polar or nonpolar compounds travel faster on silica gel?
Non polar compounds are travel faster on silica gel. Silica gel is generally used stationary phase and the empirical formula is SiO2. , The polar functional groups interacts strongly with the surface of silica gel particle while nonpolar functional groups are not interacting well.
What polarity of compound will travel the farthest on a silica gel plate?
Naphthalene