Question

5. Two unknown samples are spotted next to each other on a TLC plate. Development of the plate with ethyl acetate and visualization using UV light gives the following data: Spot 1: Rp = 0.65 Spot 2: Rp = 0.63 These two Rf values are so close that the difference might be due to experimental error (you're still learning TLC and not yet an expert in the technique). Describe an experiment that can be run using the same developing solvent (there is only ethyl acetate in the lab for some reason) to determine definitively whether these compounds are the same or not. 2 points

Answer 1

Given two unknown samples which after a run on TLC were identified with Rf values 0.63 and 0.65 which are so close.

So to confirm whether the two compound are same or different, there is one way called Co-spotting.

Experiment:

Spot the two unknown samples as spot 1 and spot 2 (say A & B) next to each other and spot the two unknown samples A&B on one another in between them. (as shown in below figure 1)

Now run the TLC with the same Ethylacetate, if the co-spot get seperated into two spots then they are two different unknown compounds (as shown in figure 2)

If the co-spot didn't get seperated into two spots they are same.

Figure 1 A A&B Spot1 Co-spot B spot2 Figure 2 solvent line А B A&B Co-spot