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Difference in peak area

Posted: Sat Dec 22, 2018 12:03 am
by phil1150
Hi,

I have analyzed a brown alga as well as rapeseed oil containing the alga in both GC-FID and GC-MS. I have used HP-5 column on the GC-FID and HP-5MS on the GC-MS (EI).

The C18:1 fatty acid peak for the alga and rapeseed oil was 73.87 and 45.70, respectively, in GC-FID.
In GC-MS the peak for the alga and rapeseed oil was 7397271832 and 62522225819, respectively.

Should the ratio between the peak areas from GC-FID not be the same as the ratio between the peak areas from GC-MS? As the fatty acid is also present in rapeseed oil, the peak areas from GC-MS sounds more plausible, as the amount of acid originate from both the alga and the oil itself.

Why do I not get a bigger peak in the oil sample from GC-FID and what could be the reason for such a difference between the ratios?

Sorry for all the question... I just find it frustrating

Thanks in advance