lose of standard

[nina]

Hi
I use standard methyl oleate for analysis of FAME.
I storage the standard in the freezer and under nitrogen gas, but now after one month peak of 50 ppm standard is very very small.
I use capric acid as a internal standard.the peak of IS dose not change.

please help me
thanks

[chromatographer1]

Bugs like butter as do I.

Bacterial contamination may be digesting your std. Of course, UV light can be a cause also. Evaporation does not seem likely as the capric ME sounds stable.

So, if you can rule out oxidation, it appears that the bugs win as far as my guess is concerned.

[nina]

Bugs like butter as do I.

Bacterial contamination may be digesting your std. Of course, UV light can be a cause also. Evaporation does not seem likely as the capric ME sounds stable.

So, if you can rule out oxidation, it appears that the bugs win as far as my guess is concerned.

thanks
I tought that light cause it, but today I change my column and solve this problem.I dont underestand reason it.
best regards

[chromatographer1]

The oleate ester is unsaturated. If you have active sites on the injector or the column you can have adsorption of the oleic acid methyl ester where the more volatile decanoic acid methyl ester will elute without much retention.

Be sure to replace injection liners and trim the front of your capillary column occasionally if you inject dirty samples.

the good news is you ran a standard to verify the column-GC is working correctly.

best wishes,

Rod