Practical investigations
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Hi, I'm doing the wine analysis and was wondering why acetic (ethanoic) acid cannot be detected by TLC. I'm using the solvent n-butanol/formic (methanoic) acid/water and the indicator bromocresol green. Thanks.
Igloo writes ...
It is found experimentally that volatile acids such as acetic acid and propanoic acid do not show up in TLC. Perhaps the reason is to do with the very fact that they are volatile, and, under the conditions of the experiment simply evaporate away into the air whilst the chromatogram is being developed. In reality you would expect very faint spots to show, since it is hard to believe that all these acids will volatilise away, but my students have never been able to find any chromatographic trace of volatile acids during TLC, and neither have I.
Another interpretation is that acetic acid (ethanoic acid) is too “similar” to the formic acid (methanoic acid) in your eluting mixture, so maybe it simply mixes into this liquid and “joins” the other solvents!
The only type of chromatography which will definitely work is that which is “enclosed”, e.g. GLC (gas-liquid chromatography), but I doubt whether you have the facilities to carry out this type of chromatography at your school/college.
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updated: 17 April 2007
