Chromatography Forum

Dear all;
I have a problem about my GC. Last week I did 2 experiments. I used extracted sample in the first experiment. For the second one, I washed the sample with solvent. I`m using DCM(dichloromethane). After GC analysis I saw that there was a contaminant at the GC chromatogram for 100. minute of the second analysis. But there was no problem about first analyse. I tried the same experiment with different samples...The result is the same...I could not find the problem.
What is your comment?

It appears that your DCM is contaminated and something is extracted from it into your sample.

best wishes,

Rodney George
consultant

Also I used CS2 as solvent, the problem is the same. There was a contaminant at 100. min?

I am not clear on what exactlly you did with your samples. You say that you first used an extract and then you washed the samles. Did you extract the samles with one solvent and then go back and reextract them with another or did you process the extract?

What kind of samples were you working with and what steps did you take? A bit more detail may help here.

I'm working for a petroleum company. We analyse core samples and determine hydrocarbons qualitatively and quantitatively.

We had a core sample. We seperate this sample two part. We extracted the first part with DCM and did GC analyse.
And than the second part was rinsed with DCM (we did not apply extraction) and did GC analyse.
I saw that there was a contaminant at 100. minute for the rinsed sample.
I repeated the rinse process with CS2. But the result was the same, I saw the contaminant at the same retention time.

You may have a surface contaminant on the core sample resulting from storage (was it stored in plastic?) or from equipment used to take the core sample. I would see what fluids and lubricants were used in the processing, taking, and handling of the core. Look at storage conditions and containers.