A students performed a TLC experiment on a mixture containing two compounds. How
ID: 894261 • Letter: A
Question
A students performed a TLC experiment on a mixture containing two compounds. However, he observed only one spot after visualizing the TLC plate with U.V. light. Give a possible explanation for the student observing only one spot. (2 pts)
TLC plates could be made of different particle size of silica. If one used a smaller particle size of silica in the TLC plate, how would that effect the results of a TLC experiment? Explain your answer. (2 points)
The type of TLC performed in lab this week is often referred to as normal phase TLC. In a reverse phase TLC, the plate is coated with C18 hydrocarbon solid and the mobile phase used often consists of methanol and acetic acid or acetone. What would be the result if one used this system for separating the pigments of spinach? Explain your answer. (4 pts)
Explanation / Answer
One compound showing the UV activity because it may be an aromatic compound, compound having conjugation. The other one is an aliphatic compound it may show the spots in the staining reagents, depending on the functional groups in the compound. If it is a amine (Ninhydrine stain), aldehydes (2,4 DNP), Alkynes and alkenes shown in KMnO4.Particle size of 1-25 microns is commonly used for the separations. The use of fine-grained silica is one of the best reasons for the better resolution in TLC. With the decrease in the particle size we can get better resolution.Using reverse phase TLC system we can seperate the carotenoids (beta-carotene, xanthophylls and chlorophylls). The solvent which is used in the reverse phase TLC is a mixture of (chloroform: methanol: water) (75:20:5). Some other solvents Acetone: water (60:40) and acetic acid and water (75:25).
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