Peaks there then gone!

Question

I am running a sample. I ran it on two separate GCS twice so a total of four runs. I saw two contamination peaks at a consistent peak area on all four chromatograms. I then ran the sample on a third different GC. The peaks vanished! I presumed the peaks weren't carry over as the peak size was consistent. But I also felt peaks can't just disappear. Any ideas?

CMZainea · Answer

I&rsquo;m sorry for the delayed reply to your message. Do you still need assistance with this? If you do, please take into consideration the notes below. However, if the issue was resolved, could you please share what the resolution was? 
 There are a few details I would need for this: 
 - are all 3 GCs the same (same model, same injection type, syringe size, inlet, column type and detector)? Somewhat related, please mention the GC model, the injection type, syringe, inlet type and the detector type. 
 - are the Aquisition Methods identical? 
 - assuming the above points are true, did you inject the sample from the same vial you injected on either of the previous 2 GCs? 
 - do the contamination peaks elute at a Retention Time expected for any of your compounds?