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4.5. Standard solutions of trimethylsilyl ethers of aliphatic alcohols from C20 to C28. They may be prepared from mixtures of pure alcohols at the time they are required for use.

Reference solution for thin-layer chromatography: C20-C28 alcohols 0,5 % in chloroform, or a fraction of alcohols obtained as indicated in point 5.2 from the unsaponifiable matter of an olive-pomace oil.

And

reference sample: pure monoglycerites or mixture of monoglycerites which the quantity in the solution is known,

something which I can translate like this. But all in the olive oil analysis (for this one, for analysing % glycerile monopalmitate).

I searched a lot but I could not find what these are exactly. We are searching for the olive oil analysis. Anyone who knows what it means?

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  • $\begingroup$ It could be more clear what exactly is the question. $\endgroup$
    – Poutnik
    Mar 7 at 11:47

1 Answer 1

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  • The first two quotes refer to solutions of aliphatic alcohols; here "C20 to C28" indicates a range of the number of carbon atoms in each of the molecules, which can be 20, 21, 22, 23, 24, 25, 26, 27, or 28. If it is a sample to eventually calibrate the GC, the supplier will document its composition, i.e. the percentage of each fraction. To reduce the risk of decomposition of the trimethylsilyl ethers, they are prepared just before their intended use.

    To illustrate the concept, Agilent is one source of such standards for GC currently compiled here. One of them is Part Number:5080-8716 to simulate a distillation with 19 analytes in reference to ASTM D2887 and ASTM D7213:

    | analyte           | concentration | CAS number |
    |-------------------+---------------+------------|
    | n-Decane          | 9.7 % (w/w)   |   124-18-5 |
    | n-Dodecane        | 19.9 % (w/w)  |   112-40-3 |
    | n-Dotriacontane   | 0.9 % (w/w)   |   544-85-4 |
    | n-Eicosane        | 1.3 % (w/w)   |   112-95-8 |
    | n-Heptadecane     | 5.2 % (w/w)   |   629-78-7 |
    | n-Heptane         | 4.6 % (w/w)   |   142-82-5 |
    | n-Hexadecane      | 10.3 % (w/w)  |   544-76-3 |
    | n-Hexane          | 4.4 % (w/w)   |   110-54-3 |
    | n-Hexatriacontane | 0.9 % (w/w)   |   630-06-8 |
    | n-Nonane          | 4.8 % (w/w)   |   111-84-2 |
    | n-Octacosane      | 0.9 % (w/w)   |   630-02-4 |
    | n-Octadecane      | 2.2 % (w/w)   |   593-45-3 |
    | n-Octane          | 4.7 % (w/w)   |   111-65-9 |
    | n-Pentadecane     | 5.1 % (w/w)   |   629-62-9 |
    | n-Pentane         | 8.2 % (w/w)   |   109-66-0 |
    | n-Tetracontane    | 0.9 % (w/w)   |  4181-95-7 |
    | n-Tetracosane     | 0.9 % (w/w)   |   646-31-1 |
    | n-Tetradecane     | 10.2 % (w/w)  |   629-59-4 |
    | n-Undecane        | 4.9 % (w/w)   |  1120-21-4 |
    

    A standard (as in protocol) usually describes the necessary equipment (as in chemicals, machinery) and procedure how to yield a specific result. ASTM, ISO, FDA are a few of larger organizations to convene and publish standards relevant to chemistry.

  • The third describes either the solution contains only one monoglycerite, or multiple monoglycerites. But in either case their concentration is known; for instance 3% by weight is monoglycerite A, 36% by weight refers to monoglycerite B.

Based on the snippets you shared, it seems possible their source is European Regulation 2019/1604 of 27 September 2019 amending Regulation (EEC) No 2568/91 on the characteristics of olive oil and olive-residue oil and on the relevant methods of analysis. In ANNEX VII, there is a section describing the required reagents for to perform the next analyses including

4.8. Silylation reagent, consisting of a 9:3:1 (V/V/V) mixture of pyridine/hexamethyl disilazane/trimethylchlorosilane.

It is followed by a description how to prepare the ethers in question and setup of the analysis (temperature of injector and detector, temperature ramp, carrier gas composition, flow, split ratio, volume of injection). Section 6.4. Peak identification, Table I listing relative retention times, and Figure 2 of an annotated chromatogram for instance name some the sterol alcohols analyzed, e.g., cholesterol ($\ce{C27H46O}$), brassicasterol ($\ce{C28H46O}$), ergosterol ($\ce{C28H44O}$); in the above definition, one C27, and two C28 alcohols.

If this European norm is the protocol you have to follow, check it again for the chemicals mentioned. (A larger public database to recognize chemicals than Wikipedia is e.g., chemspider -- if there is a public record there, it will report e.g., the Hill formula, and a structure formula.) Else, get in touch with your supervisor or/and client to identify the relevant standard to use.

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  • $\begingroup$ Buttonwood, thank you for the answer. But as a fresh beginner in laboratory, I do not have a whole understanding of what you wrote. Could you please write me these specifying how to find them (maybe chemical identity) or how to mix what kind of solvents etc.? Thank you very much. $\endgroup$
    – wise
    Mar 7 at 11:03
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    $\begingroup$ @wise The answer was amended; likely, the next work ahead of you is more evident now. And in general (not only for chemistry.stackexchange.com): if you quote, name/link the source of the information. $\endgroup$
    – Buttonwood
    Mar 7 at 16:10

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