Beginners queries

[AncientFattyAcid]

Dear all,

I was introduced into fatty acid analysis only a few moths ago.
The thing is, that I had almost no background in chemistry till then whatsoever (exept for school, but thats too long ago). My original profession is archaeology, but I am very interested in residue analysis on ancient ceramic vessels and soil.

Since I have really basic knowledge I need to put some, probably very banal questions:
1. What is the difference between qualitative and quantitative analysis?
2. What happens when you quantify samples with internal standars; or how does quantification work?
3. What can happen to the oxygen atom of a carbon chain, if it's not methylised after saponification?

Alternatively, I am always happy about literature that can help me answer this questions myself.

Thanks in advance

[rb6banjo]

1) Qualitative analysis tells you "what". Quantitative analysis tells you "how much.
2) Internal standards are usually added when you have to take your sample through a fairly rigorous preparation scheme - like a derivatization followed by an extraction/concentration to isolate your analytes. You fortify the sample with the internal standard (hopefully closely related chemically to the analyte(s)) that goes through all of the gyrations of the preparation. Internal standards are also sometimes added to samples to help normalize variability in a particular analysis technique (headspace solid-phase microextraction for instance). You have to understand the response of your instrument to changes in concentration of your analyte so that you can get quantitative numbers. See any basic quantitative analysis text book for more information.

https://en.wikipedia.org/wiki/Quantitat ... chemistry)

3) Carboxylic acids are difficult to chromatograph on most stationary phase because of the acidity of that -OH group on the functional group. Methylating it (make methyl esters) decreases the polarity of the molecule and makes it interact with most typical gas-chromatographic stationary phases in a much more predictable and reliable way.

Good luck. Perhaps others can offer some more insight for you. There's more to it but this is my "nutshell" sort of description.

[Consumer Products Guy]

3. What can happen to the oxygen atom of a carbon chain, if it's not methylised after saponification?

The oxygen atom stays, part of the methyl ester you form from the fatty acid or soap. Side-chain hydroxy group (like with ricinoleic acid) just stays "as is" with methyl ester formation.

I liked "2330" cyanopropyl silicone phases such as SP-2330 for fatty acid methyl esters used in consumer products, separated stearic ester from oleic ester readily.

[AncientFattyAcid]

Thank you very much, your answers really helped me get a better understanding!

[GOM]

Hi


This sounds interesting

Are you trying to analyse fat and oil residues and thus identify their origin?

Are they cooking or storage vessels?

What age and region?

If storage, olive oil is an obvious candidate.. there will obviously have been some oxidation/degradation

I suspect that there will be a lot of literature on this

Regards

Ralph

[AncientFattyAcid]

Hey Ralph,

I am delighted, to see other people are interested in this kind of research.
You also seem to be well informed!

To answer your questions:

Are you trying to analyse fat and oil residues and thus identify their origin?

Are they cooking or storage vessels?

What age and region?

We are working on early iron-age storage vessels, more precisely amphorae found on a site on the lebanese coast. And yes, finding out the origin is exactly what we aim to do.

If storage, olive oil is an obvious candidate.. there will obviously have been some oxidation/degradation

I suspect that there will be a lot of literature on this

The main assumption was, that this type of amphorae served for storing wine. After analysis by specialists it turned out, that no wine was stored in our vessels.
At that point our work startet, and considering the region and the climate it seems likely, that - as you pointed out - they contained olive oil. The preliminary results of some of the samples also piont to that, but as you said oxidation and degradation is an issue. It depends on what results the rest of the samples will yield, wether we send some in for stable isotope analysis, to clarify the situation.

There is some literature I know of, but I think I am yet far from having read every relevant article.

If you have further ideas and/or suggestions on that whole matter I am happy to read them.

Kind regards

E.

[GOM]

Hi E

This is indeed interesting

Thank you for the additional information

Your original post about methylation suggested that you were looking at extraction and derivatisation of oils/fats for subsequent GC analysis for identification

Before making any suggestions for GC analysis may I ask some further questions

Are you working with one amphora or a few amphorae?.

Are they complete or are you working with fragments ? Oddly enough fragments would be better. Then you would have the luxury of sacrificing a fragment for extraction derivatisation and GC analysis just to see what you get.

You mentioned the coast - are these from a shipwreck or land based? Just a thought - would oil immersed in sea water be less prone to oxidation or at least the oxidation/degradation slowed up?

Would a basic primer on oils and fats for a non chemist- their chemistry and methods of analysis be helpful?



Kind regards

Ralph

[Peter Apps]

Interesting. The people who have good skills on the chemistry of oils that have been exposed to air for hundreds of years work on old oil paintings - oil paints "dry" by oxidative polymerization.

Peter

[dianna4mail]

Hello,

We just started working for a few days in our lab with a new GC MS Agilent Technologies model 7890A, coupled with 5975C MS. We started injecting essential oils using different methods. The problem is the final peak identification. The library database only identifies the big peaks so we get only 2-maximum 4 substances. Do you have any idea how or where in the software to set the program to identify all the peaks?
Thank you for your patience...I am really a beginner...

Waiting for your respons,

Diana

[Peter Apps]

Hello,

We just started working for a few days in our lab with a new GC MS Agilent Technologies model 7890A, coupled with 5975C MS. We started injecting essential oils using different methods. The problem is the final peak identification. The library database only identifies the big peaks so we get only 2-maximum 4 substances. Do you have any idea how or where in the software to set the program to identify all the peaks?
Thank you for your patience...I am really a beginner...

Waiting for your respons,

Diana

Hello Diana

Welcome to the forum. You need to start a new thread for your question, it will not get many reads added to the end of this one.

Peter

[rb6banjo]

I can tell you that you probably need to go in and adjust your integration parameters so that the software is integrating all of the peaks you want it to integrate. Can you perform a manual search of your peaks of interest and get correct identifications?

[aaronrodg]

Thanks a bunch for this...