Sometimes these unidentified fatty acids are proportionally distributed over the other fatty acids. Is that the way how this laboratory handled these fatty acids? Hint: what is the sum of all values in the excel sheet?

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Not right. If you sum all values for fatty acids (ignoring the unidentified fatty acids) you get a value of 100%. This means that the values for fatty acids are normalized to 100%: the unidentified fatty acids are proportionally distributed over the other fatty acids. Otherwise, adding up all values (including the value for the unidentified fatty acids) will give 100%.

Right! This laboratory distributed the unidentified fatty acids proportionally over the other fatty acids. However, there is no universal way to deal with these unidentified fatty acids. Therefore, it is important to ask your lab how they handled these unidentified fatty acids. And of course the laboratory needs to report the amount of unidentified fatty acids.

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No

Yes

Here you see the results (chromatogram) of the fatty acid analysis of the margarine. Study this chromatogram together with the data in the excel file.

In the excel file with the laboratory results of the fatty acids analysis of margarine you see for several fatty acids the amount of fatty acid methyl ester (FAME) in gram per 100 gram FAME. Note that 0.9% of the fatty acids were not identified. This means that some fatty acid peaks in the chromatogram do not correspond to the retention times of identified peaks in the reference chromatogram. Therefore, these fatty acids could not be identified.