I have analyzed the sample of one Essential Oil to identify its chemical components by GC-MS. The report shows the qualitative data having R. time, I. time, F. time, area, area %, height, height %, and A/H against each identified peak. How can I calculate the percent concentration of each identified compound by using the mentioned data? Please guide.
Thanks in anticipation.
Hi Usman,
Right now you can only report Area %.
To provide quantitative results you need response factors for the compounds you wish to report. Response factors allow you to convert area% to wt% or vol%.
Agreed with Rafal Gieleciak Area %. is a direct indication of percent concentration of the chemical compounds
Ikram Madani Ahmed Thank You for your answer, Sir.
Can you please provide some relevant literature in which the authors have mentioned the area % is directly linked with the percentage concentration of each identified compound?
I need the literature as a reference, please.
Thanks and Regards
Area % is not equivalent to concentrations. From the Beer-Lambert's law the absorbance depends on concentration, pathlenght (constant in the same cromatograph, can be neglected) and molar absorptivity at a given wavelength, which is different for each compound. You have to perform calibrations for each compound at the same wavelength (not from TIC data).
Area %. refer to the main compounds in the TIC,
So the area %, is not a concentration percentage
While Dr. Davies is to some extent correct this is not quite the case. In total ion chromatography your MS is operating in a manner very similar to a FID in that you are looking at the sum of all of the ions for each peak. This is actually the most accurate way to use a MS and comes close to replicating the output of a FID.
Each compound detected has a relative response factor (RRF); that is, how big of a peak it produces for a given mass. FID response factors tend to be very similar whereas there is more variation in MS response factors. Thus, if you use the area% values in FID for something like an essential oil you will obtain a semi-quantitative result that is not too far off of a true quantification. If you use the area% values from your MS you will also obtain a semi-quantitative result but your relative error will be larger than that of the FID since there is more difference in the response factors for individual compounds for the MS than for the FID, especially when it comes to aliphatic hydrocarbons.
So, when Dr. Gieleciak says that you can only report area% since you have no response factors this is true for both the FID and the MS. In order to provide absolute quantitative results you will have to calibrate for each peak, which in essential oil analysis is, at best, impractical.
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