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Place each TLC plate in a developing chamber containing the 1:1 mixture of ethyl acetate and hexanes and allow the solvent to climb the plate until in comes with in a ½ cm of the top of the plate. Once this occurs, remove the plates from the chambers and mark the solvent fronts with a pencil. Allow the TLC plates to dry. Using a pen instead of a pencil to draw a start line might cause this as the ink can travel with the solvent system on the TLC plate. Several Unexpected Spots Seen. Dropping organic compounds accidentally on the TLC plate or touching the surface of the plate while handling it might result in unexpected spots upon developing the plate. TLC plate holder: 1: Z266027: TLC plate rack: 1: Z266043: Aluminum multi-plate racks - for use with 10 cm × 10 cm plates: 1: Z266035: Aluminum multi-plate racks - for use with 20 cm × 20 cm plates: 1: Z266078: PTFE multi-plate racks - for use with 10 cm × 10 cm plates: 1: Z266094: TLC plate storage racks - rack for 20 cm × 20 cm plates: 1. Solvent polarity on Rf. Look over the photos showing TLC on the course website. (1.) TLC analysis of analgesics. The powdered side of the silica gel plate, not the shiny, plastic side is the side that is spotted. Lightly draw a pencil line about 1 cm from the end of a plate. Use a pencil, not a pen,. Draw Tlc Plate online, free; Draw Tlc Plate Online Game; Thin-layer chromatography (TLC) is one of the basic analytical procedures in chemistry and allows the demonstration of various chemical principles in an educational setting. An often-overlooked aspect of TLC is the capability to quantify isolated target compounds in an unknown sample.

Organic compounds most commonly appear colorless on the white background of a TLC plate, which means that after running a TLC, chemists often cannot simply see where compounds are located. The compounds have to be 'visualized' after elution, which means to temporarily convert them into something visible.

Visualization methods can be either non-destructive (compound is unchanged after the process) or destructive (compound is converted into something new after the process. Viewing a TLC plate under ultraviolet light is non-destructive, while using a chemical stain is destructive.

Visualization Summary

Below is a summary of various visualization techniques, and the functional groups that generally react with each. A more detailed discussion of each technique is provided later in this section.

UV Light: For aromatics + conjugated systems	Iodine: Visualizes ~half the time. Strongly reacts with aromatics	p-Anisaldehyde: For many aldehydes, ketones, and alcohols	Vanillin: For many aldehydes, ketones, and alcohols
Permanganate: For alkenes, alkynes, or oxidizable groups (aldehydes, alcohols)	Phosphomolybdic Acid (PMA): For alcohols, phenols, alkenes, and many carbonyl compounds	Iron(III) Chloride: For phenols	Bromocresol Green: For acidic compounds

Table 2.4: Summary table for TLC visualization methods.

Ultraviolet Absorption

The most common non-destructive visualization method for TLC plates is ultraviolet (UV) light. A UV lamp can be used to shine either short-waved (left( 254 : text{nm} right)) or long-waved (left( 365 : text{nm} right)) ultraviolet light on a TLC plate with the touch of a button. Most commercially bought TLC plates contain a fluorescent material (e.g. zinc sulfide) in the silica or alumina, so the background of the plate will appear green when viewing with short-waved UV light. If a compound absorbs (254 : text{nm}) UV light, it will appear dark, as the compound prevents the fluorescent material from receiving the UV light.

This method is so quick and easy that it is often the first visualization method tried. It is most useful for visualizing aromatic compounds and highly conjugated systems, as these strongly absorb UV. Most other functional groups do not absorb UV light at the wavelengths used and will not appear dark under the UV lamp even though they are still there. It doesn't hurt to try UV after performing TLC with all compounds just in case. Since the compounds remain unchanged after viewing with UV light, a further visualization technique can be used afterwards on the same plate.

Procedure for UV visualization of TLC plate:

Use a UV lamp to look at your developed TLC plate by pressing the short-waved button. Depending on what is available at your institution, you might tilt the UV lamp at an angle in a darkened area of the room (Figure 2.31a), or you might look at the plate inside a box designed to protect eyes from UV damage (Figure 2.31b).
Safety note: Care should be taken to never look directly at the UV source, and to minimize exposure to eyes.
The plate background will appear green under short-waved UV light, and UV-active compounds will appear dark (Figure 2.31c). Use a pencil to lightly circle spots, as they will disappear when the UV light is removed.
Some compounds themselves fluoresce (Figure 2.32), appearing a variety of colors when exposed to either short- or long-waved UV light (bright purple or blue is the most common). Record these types of observations in your notebook if you see them, as they are rare, and are therefore an excellent identification tool. They are most common with highly conjugated compounds.

The TLC plate can be further visualized with some other method if desired (iodine or a chemical stain).

Iodine

A commonly used semi-destructive visualization method is to expose a developed TLC plate to iodine (left( ce{I_2} right)) vapor. An 'iodine chamber' can be created by adding a few iodine crystals to a TLC chamber, or by adding a few iodine crystals to a chamber containing a portion of powdered silica or alumina (Figure 2.33a). When a developed TLC plate is placed in the chamber and capped, the iodine sublimes and reacts with the compounds on the plate, forming yellow-brown spots (Figure 2.33d). The coloration occurs because iodine forms colored complexes with many organic compounds. This stain will work with approximately half the compounds you may encounter.

This method is considered 'semi-destructive' because complexation is reversible, and the iodine will eventually evaporate from the TLC plate, leaving the original compound behind. When the coloration fades, it is theoretically possible to use another visualization technique on the TLC plate, although it's possible the compound may have also evaporated by that time.

Procedure for visualization of TLC plate with iodine:

If not already prepared, make an 'iodine chamber' (Figure 2.33a): in a fume hood, place a few centimeters of powdered silica or alumina in a screw-capped TLC chamber and add a few crystals of solid iodine (safety note:silica and alumina are lung irritants, and iodine vapor is considered an irritant and toxic). A beaker and watch glass will not work in this context as the iodine vapors will escape. Let the silica or alumina and iodine sit together for a while with periodic swirling, and eventually the powder will become orange from adsorbing the iodine vapor.
In a fume hood, place the developed TLC plate in the iodine chamber with forceps (Figure 2.33b) and close the lid. Gently shake the chamber to bury the TLC plate in the iodine-stained silica or alumina (Figure 2.33c) until the spots become colored (Figure 2.33d). Many spots will appear yellow-brown almost immediately, and may darken with extended time. For many compounds, it takes less than 10 seconds to develop a plate, but some compounds require 10 minutes or longer. (Note: alcohols, carboxylic acids, and alkyl halides often do not stain.)
Promptly record appropriate observations of the TLC in your notebook, or circle the spots with a pencil, as the colors will soon fade as the iodine evaporates from the plate. Further visualization may be attempted after the color fades.

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