Chromatography Forum

Hi all!

Basically, I analyze essential and fatty oils (raw material) for pharmaceutical use, using GC-FID equipment and European Pharmacopoeia methods.
My equipment is Agilent GC 7820A with autosampler Agilent G4513A.

And I have some problems with Castor oil (virgin) identification C: identification of fatty acids (method number 01/2013:0051).


In method is written that I need to correct peak by multiplying it by a correction factor, that I calculate from the result of Reference solution analysis.
But i fact, the result of analysis that gave me my ChemStation, automatically calculating content percentage (program is not taking in account solvent peak), is closer to analysis result that gave us company manufacturer.

For example last Castor oil component percentage was:

company manufacturer analisys results:
-palmitic acid - 1.2%
-stearic acid - 1.4%
-oleic acid and isomers - 3.8%
-linoleic acid - 5.0%
-linolenic acid - 0.5%
-eicosenoic acid - 0.3%
-ricinoleic acid - 87.4%
-any other fatty acid - 0.4%

from ChemStation (automatical calculation)
-palmitic acid - 1.1%
-stearic acid - 1.3%
-oleic acid and isomers - 3.6%
-linoleic acid - 4.6%
-linolenic acid - 0.4%
-eicosenoic acid - 0.3%
-ricinoleic acid - 88.1%
-any other fatty acid - 0.5%

with correction:
-palmitic acid - 1.0%
-stearic acid - 1.1%
-oleic acid and isomers - 3.1%
-linoleic acid - 3.9%
-linolenic acid - 0.4%
-eicosenoic acid - 0.3%
-ricinoleic acid - 89.8%
-any other fatty acid - 0.5%

Correction factor is 1.19.

Why could such big difference appeared between company manufacturer results and my with correction?
And what peak I need to multiply by correction factor, all?

Cheers,
Dmitrij

Hi Dmitrij

I will venture to make the following comments

1. The correction factor is applied because the presence of O in the OH group of ricinoleic acid methyl ester reduces the effective carbon number and thus the response in the FID. The correction factor is thus >1, which it is.

2. The correction factor is only applied to the methyl ricinoleate peak, which you have done. If you applied it to all the peaks, as you asked, you would end up with the original answer

3. What is the repeatability of your procedure? Small errors at each stage can add up and are more noticeable at the 90% level and seem worse than the same error at the 0.9% level

4. What is the reproducibility of the method? We don't know.

5. Are the manufacturers using exactly the same method?

6. Both results are within the specification.

Regards

Ralph

Your results look pretty good to me.

Someone here posted "Never trouble trouble until trouble troubles you"