h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

hi. im a 6th year student and would like to try thin layer chromatography to find out which acids are present in various types of vinegar(malt, cider..etc..). i was wondering if anyone here could tell me how could i go about doing this and what solvent should i use? thanks.

The main acid in any vinegar will be acetic acid (ethanoic acid). So you'll have a major peak for that, anyway.

It's a good while since I've done TLC. Acetic acid is soluble in water, but any longer-chained acids which may possibly be present probably wouldn't be (or, wouldn't be very much). So with an aqueous solvent you'd get acetic acid fairly near the top of the plate, and any others fairly near the bottom. But all the others may be in a single peak all on top of each other (that's a guess, and may be wildly inaccurate). So adding something to the solvent mix to which they'd be more attracted may help to resolve them. How about methanol? It's organic, polar, and miscible with water.

(Methanoic acid is the only organic acid which is shorter-chained than ethanoic acid. All others would have longer chains. What acids are you expecting to find?)

TRiG.

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Do you?


As TRiG said, they won't be terribly soluble in water - as is. You could try dissolving them into the water using a mildly basic solution, that should strip the proton of, make the acid ionic, and boost the water solubility. How basic of a solution can you use with TLC?

Also, you might try acetone as a solvent, it's somewhat polar.

i think should find ethanoic, tartaric, malic, lactic, citric and succinic acid. Nadia

In a method for separating salicylic acid by tlc, ethanol is used. This would also dissolve longer chain acids.