Chromatography Forum

Can any one help me on triglyceride analysis using gc fid? I am using restek 65tg column. Is the triglyceride standard decompose quickly?
Peaks are not appearing sharply.

Sure, I've assayed intact triglycerides in consumer products, at maybe 0.25 to 5% by capillary GC-FID. I used a specialty high-temperature capillary, a stainless steel capillary, from Restek, and high temperatures.
https://blog.restek.com/wp-content/uplo ... S1368A.pdf

As to sharpness, remember that there are positional isomers too, like a triglyceride with only palmitic and stearic chains can be 16-18-18, 18-16-18, 16-16-18, or 16-18-16 ....

Do we need to use programmable injector port for that? Is Shimadzu 2014 gc model used to programme injector port?

I used the regular Agilent injector and injection port.

The only intact triglycerides I've done are artificial medium chains (C8/C10 Neobee) I see 4 peaks on a normal db5 column taken to 325 deg C. glycerol: (C8)3; (C8)2(C10); (C8)1(C10)2 and(C10)3.

T24 to T32 triglyceride are appearing very sharply in gc. But T34 to T54 is not appearing properly.Before each injection I have melt the std as its solidify in room temperature.

I have been following this thread with interest due to my background in this analysis, which is very similar to that of Consumer products guy.

Is the triglyceride standard decompose quickly? No

CPG also made some pertinent comments about the complexity of the positional isomers

Perhaps if you could explain exactly with more details of the sample, your aim in the analysis, your equipment, conditions and post an example chromatogram ?

and also clarify your comment

Before each injection I have melt the std as its solidify in room temperature.

Please reassure me that you are not trying to inject a neat triglyceride

Ralph has made some good points.

In addition to taking the column to 375C or more, we also made the inlet 375C or more. And we always dissolved the triglycerides in solvent too.

Note that I worked with consumer products, and sometimes candles contain triglycerides or hydrogenated triglycerides.

We purchased triglycerides and split them into fatty acids for soap making, so most often we assayed fatty acid distribution as the FA methyl esters.

I am using anhydrous butter fat standard. Shimadzu GC2014 with FID ; column is restek 65tg. Inlet temp 350°C, oven goes up to 365°C and detector is 370°C and run time aroung 42mins.
10% butter fat with 0.5 microl injection volume and split ratio is 50.1.

I want to find milk purity using triglycerides; according to ISO Standard.
Low molar mass triglyceride appearing but high molar mass triglyceride are not eluting properly.
I hope to increase the flow rate to elute higher triglycerides.
Thank you very much for helping me.

It's true that the TAGs will be a mixture of isomers, but that's not really the reason for the poor peak shape. We were analyzing synthetic TAGs which were regiochemically pure (i.e., pure SOS, pure SSO, etc.) and observed the same poor peak shape for peaks of TAGs beyond OOO. POP, PPO, etc. looked great. We were able to improve on the peak shape a bit compared to the published chromatograms for cocoa butter TAGs, but eventually gave up and switched to non-aqueous reversed-phase HPLC for analysis. For the bigger TAGs, you're really pushing the "Gas" of gas chromatography if you're doing split/splitless. We weren't able to evaluate cold on-column injection, but from what I've seen, it doesn't improve peak shape much.

Thanks for all. Now triglyceride peak pattern is coming. I changed the column. Agilent 5 ht column. But when I calculate S values according to ISO standard it is not perfectly match with the standard. Can we guess the adulteration using the pattern of milk triglyceride?

Buenas noches amigo, de mi parte he analizado trigliceridos pero en pequeñas cantidades por el metodo de contenido de glicerina, mono, di y triglicerido. Si estas buscando una adulteracion te aconsejo primero aplicar indice de acidez para ver cuantos acidos grasos libres hay y despues indice de saponificacion para calcular cuantos mono, di y trigliceridos hay. Si tienes una composicion esperada de tu muestra puedes saber el indice de saponificacion teorica y la comparas con el indice de saponificacion que hallaste en el laboratorio. En el caso que difieran mucho pasa montar un metodo por cromatografia acoplado a masas, el te dira que es cada señal.

Saludos