Ideally one should run a standard FAME mixture together with the two internal standards (e.g. C13:0 and C19:0) and from that calculate a conversion coefficient for each individual FAME (that is the ratio area of a given FAME to the area of the internal standard (you can plot it for each internal standard). Then you should inject the "unknown" sample without the internal standards to be sure that no C13:0 or C19:0 occurs in the sample naturally. After this control you can use the internal standards without any concern. Now, using the conversion coefficients you will obtain accurate calculations for the relative composition.

If you do not have the possibility to use a standard FAME mixture you should be aware that differences could occur in the response (area) of individual fatty acids.

Ideally one should run a standard FAME mixture together with the two internal standards (e.g. C13:0 and C19:0) and from that calculate a conversion coefficient for each individual FAME (that is the ratio area of a given FAME to the area of the internal standard (you can plot it for each internal standard). Then you should inject the "unknown" sample without the internal standards to be sure that no C13:0 or C19:0 occurs in the sample naturally. After this control you can use the internal standards without any concern. Now, using the conversion coefficients you will obtain accurate calculations for the relative composition.

If you do not have the possibility to use a standard FAME mixture you should be aware that differences could occur in the response (area) of individual fatty acids.

The peak areas will tell you the content of each of the FAME which if you add up should give you % composition.

Hi Stephen,

Yannis has answered you very nicely however I would like to add some comments: First of all you should run a FAME mix to calculate response factors (Yannis´ conversion coefficient). With this you calibrate your MS response. This will give you a factor to correct your areas in order the MS is giving different signals to each fatty acid (and it does!). Only with this correction you may express your results as "area percent". Ok, them you check if your samples has your C13 and your C19. If not or the percent are low (

Thanks for the responses. I did not mention that we had used a fame and bame library as to at least identify the respective peaks. I understood the calculation as you have described above. Unfortunately I had run the experiments in a previous lab and was not able to run standards and wont be able to run them again. Was wondering if there was a way to express the data without those standards.

But as I understand from your responses that is not possible to use the raw peak data in anyway. I had hoped i could do it like Jai had suggested but was not sure if that is accurate.

Thanks again for the clear responses.

Hi Stephen,

Jai is right but the results would not be accurate.

Hi Stephen,

Like the people mentioned above ideally you should use calibrated external standards otherwise you will only get the relative percentage concentration of fatty acids

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