Problem with Recovery

[chemistab]

I try to determine cyclohexanone and 1-dodecanethiol in a drug substance by GC-FID.
The resolution and the peak shape are good. The repeatability is also good. My problem is about recovery. I have changed liner and septum. I have also added internal standard but my problem was not solved.
Note that cyclohexanone's concentration is 70 ppm, I.S. 50 ppm and 1-dodecanethiol 5 ppm.

Any Suggestion please?

[Don_Hilton]

A bit more detail would be helpful. There are may places material can be lost between the weighed sample and the GC detector. And, many of them are before the GC inlet. Give us some idea of what is going on from the time you weigh the sample forward. And, tell us how you measured the recovery -- compared what to what.

[chemistab]

I have no pretreatment of sample.
I prepare spiked sample by dissolving 1 g of sample in diluent, adding 1 mL of stock standard solution and further diluting to a total volume of 10 mL with diluent. I prepare standard solution by adding 1 mL of stock standard solution into a 10 mL volumetric flask and diluting to the volume. I also run a blank sample in order to see if the sample contains some amount of cyclohexanone or 1-dodecanethiol.

[Don_Hilton]

Is there any functionality in the sample that could react with these two compunds? If the sample can form a ketal or hemiketal, you will suffer some losses of the ketone.

Again, it is all in the details. What is the matrix, what solvent, etc.

[kalidassa]

Hai this is kalidass may known what is the diluent you are using for that study. Because diluent plays a majar role in recovery. After knowing the diluent only we can come to a coclution for your recovery problem

Thank you
A.Kalidass