urgent chemistry question!! a level

You are correct that TLC can be used to separate other compounds, including alcohols. However, in the context of this experiment, the students were specifically looking to confirm that aspartame had been hydrolysed to produce aspartic acid and phenylalanine. TLC was used to separate and identify these two amino acids, not the alcohol that may have been present in the original aspartame molecule.
To carry out the chromatography experiment, the students would need to follow these steps:
1. Prepare the chromatography paper by drawing a horizontal line about 1 cm from the bottom of the paper using a pencil.
2. Using a capillary tube, spot the solution from the hydrolysis reaction onto the chromatography paper just above the pencil line.
3. Allow the spot to dry completely.
4. Place the chromatography paper into a developing chamber with a small amount of solvent in the bottom of the chamber. The solvent should be just below the pencil line.
5. Cover the developing chamber with a lid to prevent evaporation and allow the solvent to move up the paper.
6. Once the solvent has moved up the paper, remove the chromatography paper from the chamber and allow it to dry completely.
7. Observe the chromatogram under UV light or by spraying with a suitable reagent.
If hydrolysis has taken place, the aspartame will have been broken down into aspartic acid and phenylalanine. Aspartic acid and phenylalanine are both amino acids and will have different Rf values on the chromatography paper. The students can compare the Rf values of the spots on the chromatography paper to the Rf values of known standards of aspartic acid and phenylalanine to confirm their identities. If the spots on the chromatography paper match the Rf values of known standards of aspartic acid and phenylalanine, then hydrolysis has taken place and the aspartame has been broken down into its constituent amino acids.
I hoped this helped you, feel free to message me if you have any other questions

You're correct that the hydrolysis of aspartame produces methanol in addition to aspartic acid and phenylalanine. Methanol is a polar molecule, so it could potentially move up the chromatography paper with the solvent. However, the Rf value of methanol is likely to be very different from the Rf values of aspartic acid and phenylalanine, so it would be easy to distinguish between the three compounds on the chromatogram.
The reason why the mark scheme only accepts aspartame and the two amino acids is likely because those are the three compounds that the students were specifically looking for in this experiment. Methanol is not relevant to the question of whether or not hydrolysis has taken place, since it is a product of the reaction rather than a reactant.
To summarise my point, while methanol could potentially be separated on the TLC plate, it is not relevant to the specific question being asked in this experiment, which is to confirm the hydrolysis of aspartame into aspartic acid and phenylalanine. I hope you understand otherwise feel free to ask anymore questions (can be any subject)l