Chromatography Forum

Hi everybody,

We have a GC method for Acetic acid, where we are using tridecane as Internal standard.We did some of the samples analysis 2 years back, where we don't have any problem. Last 4 days I am trying to inject my samples , but I can't see the Internal standard peak in the sample matrix. Standards came out very good. When it comes to samples the internal standard peak is completely disappearing.

My diluent is 1.0% Citric acid in Acetonitrile. and my sample concentration is 0.2 gr in 10 ml.
I am using classical GC injector.My column is DB-FFAP 30m

Why the method worked 2 years back and not working now. Am I missing something with system setup or this is only problem with my drug substance?

Any advice please.....

Thanks

Which kind of solvent system do you choose to dissolve the standards? also 0.1%citric acid in ACN?
And I wonder if you use the completely same condition and method with you did two years before.
According to your words I think it maybe has got some problems when you treat your sample. Please check out if the ISTD amount you added is correct and try to find if you loose your ISTD in your treating period.(since I do not know how you treat you sample, use SPE; heating.....)
Wish you can solve the problem.

Hai this is kalidass,
Have you try the same with some new column? are you filtering the sample matrix before injection? have you checked your injection liner check whether glass wool is there are not. while doing this kind of on column injection glass wool is mandatory.

We are also done lot method validation for the content of Acetic Acid in APIs. Diluent as DMSO or DMF we will filter the sample matrix.

Regards

A.Kalidass

Thanks for your replies. I tried all these options i.e. Liner changed, glass wool changed.

Sample preparation is simply 0.2gr in 10ml vf, add 1.0ml of ISTD solution, and add 2.0ml of Acetonitrile and dilute to volume with 0.1% oxalic acid in acetonitrile. Finally I am taking clear supernant layer or filtering the solution.

Perhaps you have changed the phase thickness of your column or you are not having the injector at the same temperature as before.

If a simple alkane is not eluting as it did before then SOMETHING HAS CHANGED.

The original conditions may not have been recorded correctly or something in your GC is not actually at the temperature that it is supposed to be.

Tridecane was not added, or inj temp or det temp or column phase or its thickness or length but something is different.

best wishes,

Rod

Hi,
Just wonder why dont you try acetic acid content by HPLC. Its quite easy rather than using GC.

Hi,
Just wonder why dont you try acetic acid content by HPLC. Its quite easy rather than using GC.

That's what we would do here.