Chromatography Forum

Hi, I found my self in a state of confusion and can't decide which internal standard to use for my FAEE sample anaylis using GC-FID. Most Journal employed methyl heptadecanoate ester (methylic IS) (C17:0) as internal standard to analysed FAME.

is that possible if i used Methyl heptadecanoate as IS to analyse my Ethyl ester biodiesel sample (i use ethanol for transesterfication instead of methanol). I also decide to use ethyl oleate as Individual Standard. Can anyone help me explain further on this matter? Any suggestion? I really appreciate your help.


-y-

What is you sample? I'm surprised you would choose ethyl oleate as an IS because it is naturally occurring. The fatty acids with odd carbons generally are not found in samples coming from nature. That's why they are chosen as internal standards.

Generally, I add my internal standard and carry it through the derivatization procedure. So, I add C15 (pentadecanoic) or C17 (heptadecanoic) acids to the sample before I start the methylation (I use MeOH:BF3). If you add methyheptadecanoate to your sample and then transesterify the sample with ethanol and your catalyst, you will also transesterify the methylheptadecanoate.

I am usually looking for trace amounts of vegetable oil in a substantially aqueous matrix. I extract the oil (and the IS) from the matrix using C18 solid-phase extraction. I reconstitute the extract and gently evaporate the solvent. I add the MeOH:BF3 to the residue to liberate the acids and esterify them and then use SPE to isolate the FAMEs for injection into the GC.

I'm surprised you would choose ethyl oleate as an IS because it is naturally occurring. The fatty acids with odd carbons generally are not found in samples coming from nature. That's why they are chosen as internal standards.

Generally, I add my internal standard and carry it through the derivatization procedure. So, I add C15 (pentadecanoic) or C17 (heptadecanoic) acids to the sample before I start the methylation

Agree with above. I would either use C13, C15, or C17 fatty acids OR THEIR ETHYL ESTERS as internal standard. You can make your own ethyl ester of these, or purchase; I believe Nu-Chek Prep sells those.

And why make ethyl esters instead of methyl esters? We primarily did these as methyl esters, played with isopropyl esters a little bit.

What is you sample? I'm surprised you would choose ethyl oleate as an IS because it is naturally occurring. The fatty acids with odd carbons generally are not found in samples coming from nature. That's why they are chosen as internal standards.

My sample is a biodiesel produced from palm oil and triolein. i want to investigate the performance of my heterogeneous catalyst to convert the triglycerides. I also plan to use methanol for the transesterfication.

so, mean that i can choose to use methyl heptadecanoate as internal standard even my alcohol type is Ethanol (sample will be Ethyl esters?)

i'm quite noob with the GC analysis. Thank you for helping me. I really appreciate it!

Agree with above. I would either use C13, C15, or C17 fatty acids OR THEIR ETHYL ESTERS as internal standard. You can make your own ethyl ester of these, or purchase; I believe Nu-Chek Prep sells those.

And why make ethyl esters instead of methyl esters? We primarily did these as methyl esters, played with isopropyl esters a little bit.

I checked in Sigma Aldrich website catalog, They stop supply "ethyl heptadecanoate (C17).

Why ethanol? well, we are focusing on reducing environmental issues. ethanol is non toxic, quickly biodegradable and ethanol blended fuel can reduce greenhouse gas. in addition, the catalyst we use are heterogeneous which produce from natural fiber. The waste disposal problem for catalyst and ethanol will be reduce as both are biodegradable.

Sir, Thank you for your suggestion. Do you have any suggestion , as i really have a little knowledge on GC analysis. Previously, we did analysis using HPLC.

My sample is a biodiesel produced from palm oil and triolein. i want to investigate the performance of my heterogeneous catalyst to convert the triglycerides. I also plan to use methanol for the transesterfication.

so, mean that i can choose to use methyl heptadecanoate as internal standard even my alcohol type is Ethanol (sample will be Ethyl esters?)

i'm quite noob with the GC analysis. Thank you for helping me. I really appreciate it!

I'm confused. You state you "plan to use methanol for the transesterfication" and later state that your "alcohol type is Ethanol (sample will be Ethyl esters?)"

Stay all ethanol or stay or all methanol. Use heptadecanoic acid as the internal standard. If use use methyl heptadecanoate and use ethanol as solvent, be ready for some transesterification.


You've been forewarned!