Distinguishing and determining concentration of organic molecules

[jaydee]

So this m/c question came up about 2 solutions. one is ethanoic acid and one is ethanol. Which instrument is most suitable to distinguish and determine the concentration. the options were GC, H NMR, IR and AAS. Well clearly it isn't AAS and H NMR isn't the most convenient way. I thought the answer would be IR but apparently its GC. Can anyone explain why? Is IR able to determine concentration or is only GC able to since you can plot a calibration curve?

[stonecold]

Not 100% sure on this because I haven't done chem in ages...but I think IR can only be used to identify molecules by using the respective wavenumber for different functional groups.  It gives no info about concentration.

GC on the other hand can identify molecules because different molecules will have different retention times, and also, the area under the curve in a gas chromatogram can be used to calculate concentration.

[jaydee]

oh ok thanks! i think the bit about determining the concentration swung it in GC's favour. Usually you'd use IR to separate carboxylic acids and alcohols right?