Sweet TLC hydrolysis

Aspartame sweetener is a modified dipeptide. When aspartame is reacted with 6M hydrochloric acid the peptide bond should be hydrolysed (broken), producing aspartic acid and phenylalanine methyl ester. The methyl ester may also be hydrolysed, depending on the severity of the conditions.

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Whiteboard of the aspartame hydrolysis by my friend and colleague Tony Pluck

We carried out a hydrolysis reaction by boiling aspartame sweetener (one individual sachet) with 10ml of 6M HCl in a boiling water bath for 30 minutes. The results were analysed using thin layer silica chromatography, (silica TLC).

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Running a chromatogram (silica TLC plate)

Samples of aspartame sweetener were spotted before and after the hydrolysis, together with phenylalanine and aspartic acid standards.

The plate was run in a solvent system of butan-1-ol (12ml), glacial acetic acid (3ml) and distilled water (6ml) taken from the old Nuffield A’level Chemistry textbook .

After allowing the solvent to run up to within a few cm of the top of the plate it was removed from the beaker and dried using a hot hair dryer. The TLC plate was then sprayed with ninhydrin and heated in an oven at 110 C for approximately 10 minutes.

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Samples left to right, phenylalanine, hydrolysis mixture, aspartic acid and aspartame sweetener.

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Same as the above with labels on the plate

Another experiment was carried out, identical to the above except with a much shorter hydrolysis time (of about 3 minutes). This was to see if the whole experiment could be done in a 55 minute period of chemistry at school.

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The same again with a much shorter hydrolysis time of a few minutes

We want to run further chromatograms spotting smaller samples, as both of the above plates suffered from streaking due to sample overloading.