a gas chromatogram of the organic componenets of a sample of beer using a column

Question

a gas chromatogram of the organic componenets of a sample of beer using a column that separates compounds on the bassis of their relative boiling points provides a GLC trace with several peaks. Two of the smaller peaks, with retention times of 9.56 and 16.23 minutes are believed to be ethyl acetate and ethyl butyrate, respectively. -from the above information, which component of the sample, ethyl acetate or ethyl butyrate, elutes faster? what are the reported boiling points of these two substances? -what GLC experiment(s) could you perform to confirm the identity of the peaks at 9.56 and 16.23 minutes?

Explanation / Answer

You can confirm the identity of the peaks is by the use of standards. To do this, you will need a pure sample of ethyl acetate and a pure sample of ethyl butyrate. Firstly, you can determine the retention times of each of the pure samples. If these match the retention times you have already determined, then this is a reasonably good confirmation that the peaks in the beer sample are due to ethyl acetate and ethyl butyrate. However, retention times can vary from run to run. Therefore, it might be necessary to obtain further confirmation by using your pure samples as internal standards to spike the beer sample. Take one volume of the beer sample and add a volume of ethyl acetate to it. Using the same GC, obtain a gas chromatogram of the mixture. If the peak at 9.56 minutes increases in size and percent composition compared to the chromatograph for beer alone, it is quite likely that it is due to ethyl acetate. Repeat the same procedure, this time adding a volume of ethyl butyrate to a volume of beer. If the peak at 16.23 minutes increases in size and percent composition, it is quite likely that it is due to ethyl butyrate. However, many compounds have similar retention times. A better confirmation can be obtained if you use the GC separate out the two components (making use of what you know about their retention times and elution rates) and then use another technique to identify them. For example, you could do mass spectroscopy on each of your separated components and each of your pure samples and see if there is a match in the results. This is why GC is so often coupled with mass spectroscopy (GC/MS) as an analytical technique

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