Hey,

I guess it depends if your samples contain a myristic acid methyl ester?! If yes, you need the deuterium labeld form. If no, I think it is ok.

However, you should always use an internal standard very similar to your analytes - consider that! I don't know which analytes are you interested in...

Thank you so much dear Dr Benedikt Engel ,

As far as I know, blood specimen does not contain myristic acid methyl ester.

Actually, I'm interested in amino acids and carbohydrates. I want to check status of them in blood samples....

What then is the purpose of using myristic acid methyl ester if you are following amino acids and carbohydrates in blood? Are you performing dilution and SPE?

As long as a compound is not naturally present in the sample and it behaves close to your target analyte in term of partition coefficient and retention time, you can use it as the IS. Isotopic standard meet this criterion the most. However it is not the only one.

Dear Bruce Neagle ,

Actually, I want to apply untargeted metabolomics from human plasma. I'm Performing Pro. Fiehn protocol for blood sample extraction and derivatization.

In that protocol deuterium labeled myristic acid, methyl ester, defines as an IS.

Now, I would like to know that would it be correct if I use non-isotopic myristic acid, methyl ester instead of perdeuterated myristic acid or not?

Dear Dr Narong Chamkasem ,

I appreciate your taking the time to answer my question.

Depends on your method of analyse. I have not seen this protocol but I would say probably NOT. Generally, carbohydrates are derivatized to TMS (trimethyl silyl) derivatives. If carbohydrates are not derivatized they are polar and ‘water loving’ while the IS you are using is non-polar and is used in FAME (fatty acid methyl esters) analysis of oils. Solubility will be a problem and obtaining quantitative results.

Dear Bruce Neagle ,

I appreciate your taking the time to answer my question.

Dear Raziyeh,

we usually find myristic acid in plasma samples. That's why Fiehn protocol uses a deuterated standard.

Dear Claudia Fattuoni ,

thank you so much for answer.

Exactly you're right we usually find myristic acid in plasma samples. But plasma samples do not contain "myristic acid methyl ester".

Would you please send me the citation of the used protocol?

Dear Claudia,

Please see attached file.

You can find labeled -myristic acid methyl ester as an internal Standard for locking method at page 32

On pag 32 I found:

"Myristic acid d27 (Product # 366889; Sigma- Aldrich, St. Louis, MO).

https://www.sigmaaldrich.com/catalog/search?term=366889&interface=All&N=0&mode=match%20partialmax&lang=it®ion=IT&focus=product

This is not a methyl esther but the free acid: it will be silylated together with all other metabolites by treatment with MSTFA.

So, what do you think is it possible to use myristic acid methyl ester, to locking my method...?! We don't have it in the plasma

You can use whatever you want: first consider if the chosen RTL compound falls in a crowded zone of the chromatogram. If you have myristic acid methyl esther, then try it, but are you sure you need RTL? Are you frequently changing column? Or are you simply following the reported Fiehn protocol step by step?

This may be of some help

Dear Claudia,

thank you so much for taking time out to answer my question and helping me. I especially appreciate the information and advice you have provided and shared with me.

Warm regards

It might be a good idea to do an experiment to check the stability of your intended IS i.e. myristic acid methyl ester in the plasma to make sure it's not getting oxidized to myristic acid. I understand the limitation of getting an isotopically labeled IS. Have you thought about using a synthetic small molecule which has very almost zero chances to be present in plasma sample?

Dear Navid Jubaer ,

Thank you so much.

No I haven't. which synthetic small molecules do you suggest ?

Hi, This is a very interesting and relevant question for the entire research community working in metabolomics. Please feel free to register (for free to create a login with your Email ID!) and join the International Metabolomics Society’s Forum: http://www.metabolomics-forum.com/index.php?action=forum;?action=forum#c12 to ask more specific questions any software, database, approach and platform (mass spectrometry, NMR) issues where you can get very specific responses from expert users and researchers! Thanks again, Biswa