We are working on Microalgal bio diesel. For FAME analysis GC-FID (model 7890 GC (Agilent) equipped with HP-5 column) was carried out without internal standard. So from peak area and RT how we can measure the concentration of particular compound.
Hi Safar,
Quantitation without internal standard in GC is tricky and often not yielding the kost reliable reults,in my opinion. However, in order to quantify a peak, you will have to be able to compare it to a peak of known concentration.
In case you are running the Supelco-37 FAME standard for RT identification, you can use this syandard for quantification. Sigma-Aldrich supply a certificate of analysis for this standard with individual concentrations of each FAME. If you ruthis standard under the same conditions as your sample it givrs you a way of quantifying your compounds.
If you are planning on performing a lot of FAME analysis, I would recommend you investigating in an internal standard thst suits your needs. C23:0 is a popular choice for this.
Good luck!
You will need a standard to do so...It doesnt have to be an internal one....but you will need to inject a standard with known concentration to be able to relate peak area and concentration. Good luck!!
Dear Safder,
1st of all you have to Identify the compound which is done in two ways
(1) is the same method as Sabine Harrison and Carlos Frederico quoted. You have to run the standard which gives you a peak at particular RT. Than you have to run the samples to look into that particular RT and Quantify them through linear regression of the standard.
(2) option works only when your GC-FID is coupled with MS. In this case the MS will give you the exact masses of the compound and structure which can be further confirmed and quantified through online databases.
Good look
Hello, Safdar....
Only to be on the sure side...yes, you may use GC-FID to quantify your compounds, but identification is only by GC-MS...Even if your peak of interess has the same RT of the standard it only gives you a reasonable certainity...to be 100% sure, you must do as Hammad Ismail pointed out...GC-MS or another identification method. Good luck.
Safdar, if your internal standard has the same RT as one of your peaks of interes then you will need to run the standard alone. If it doesnt overlap, then you can run it into your sample. Good luck.
Run internal standards first then samples. compare RTs for each component, if they match which is very likely, then compare the peaks. You can consult EN 14105 or ASTM D 6584 standards which will guide you how to determine the concentrations of each component.
Good Luck
Hi Safdar,
As mentioned above, you will have to run the ISTD alone to establish it does not elute at the same RT as a compound in your sample. Once you have confirmed this, you will need to spike every sample with a known concentration of ISTD to allow quantitation.
In the event your chosen ISTD co-elutes with a compound in your sample, try to use a different ISTD. Traditionally used ISTDs in FAME analysis are odd-numbered long fatty acids as they are not present in nature. Hence, C23:0 is commonly used and we never had issues with it. However, I have also seen C13:0 as an ISTD.
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