detection problem in FAME analyses with Agilent 7890 GC-FID

[esn_otk]

3 months ago i had a detection problem with my GC. I couldn't see lower peaks like arachidic acid and behenic acid. I called Agilent. Service engineer checked the machine and said everything looks allright. Then i changed the colon (HP-88) everything was perfect. My proficiency test results were also perfect.

But now i have the same problem again. I haven't done much analyses on the other hand I can't detect the lower peaks. again...

Is there anything i can do? Do you have any experience about it?

[Consumer Products Guy]

I couldn't see lower peaks like arachidic acid and behenic acid.

"lower"? what range of fatty acid methyl esters are you looking for? You're making into methyl esters, not running as fatty acids, correct?

Then i changed the colon (HP-88) everything was perfect. My proficiency test results were also perfect.

But now i have the same problem again. I haven't done much analyses on the other hand I can't detect the lower peaks. again...

Try a different new column; sounds like that is the only difference, if I understand correctly.

[esn_otk]

Thank you for your answer. The worst peak is behenic acid peak. It should be between %0.3-1.5 but my results are hardly %0.1. Also stearic acid peak is so close to oleic acid peak. They don't seperate well.

I use a method which contains methylisation process with KOH-MeOH solution (13.1 g KOH in 100mL absolute MeOH).

It is nearly 4 years that I've been using the same machine and same method. In last six months the jet was changed with new one. The colon also a new HP-88. I don't know what to do/change..

[Peter Apps]

When did you last do inlet maintenance ?

Peter

[esn_otk]

When did you last do inlet maintenance ?

Peter

Last year on March.

Finally I got the solution. An agilent member called me today and adviced to cut the colon 20 cm. Everything is quite fine again. He said KOH gives harm to the colon.

[Consumer Products Guy]

We always made methyl esters using BF3 or sulfuric acid in methanol, so I never even tried injecting basic solutions; besides base tends to help saponification.

When we had triglycerides, I'd saponify first, then add BF3-methanol or sulfuric acid-methanol to esterify, then extract esters into nonpolar solvent to inject.

If you refer to your injected analytes as the methyl esters instead of the fatty acids, it may be less confusing. Our plant workers typically used the terms fat and fatty acids as the same, which made things very confusing and did cause some issues, because the plant actually bought fats and split those into fatty acids.

[Peter Apps]

When did you last do inlet maintenance ?

Peter

Last year on March.

Finally I got the solution. An agilent member called me today and adviced to cut the colon 20 cm. Everything is quite fine again. He said KOH gives harm to the colon.

There is something wrong with your sample prep if the KOH is reaching the column.

Also, it would be a good idea to change the inlet liner and septum more than once a year.

Finally; it is a COLUMN, not a colon. A colon is the fat part of a digestive system.

Peter

[Consumer Products Guy]

Finally; it is a COLUMN, not a colon. A colon is the fat part of a digestive system.

Or this :

And a semi-colon is this ; or a colon that has had surgery!