Why do peaks in blank appear smaller when a sample is present in the same diluent solvent?

I'm running acetone. It appears to have a small amount of methanol and toluene. Exactly the thing I'm looking for in the sample. When I run the acetone blank and then run the sample in the same acetone the peaks don't like exactly the same. They are smaller. Why is this? Even the main solvent peak is broader in the blank. Any help appreciated 

  • Hello  , thank you for your message.

    I would like to make sure that I am understanding this correctly. You are running a method that uses acetone as solvent. And the sample you are analyzing contains methanol and toluene?  Are those 2 peaks the only things you are looking for in your sample or is there something else as well?

    From what I understand, when you are running your blank you still see some methanol and toluene, but you shouldn't?. If this is the case, it could be that either the blank is contaminated, or that you have some carryover from previous samples (contamination in the GC system). 

    If you are running blanks from re-used vials, I would suggest trying a new vial first and see if you are getting the same problem. I would also suggest running a set of at least 5 blanks to see if the methanol and toluene decrease at all, or if they stay constant.

    For the second part of the question, are you saying that the methanol and toluene peaks are smaller when analyzing sample in acetone than when you run blanks, or the other way around?

    Regardless, are you using the same acetone bottle for the blanks and the samples?

    Please provide details of the configuration of your GC: Injection type, inlet, detector, GC model for example.

  • how much smaller are the peaks?
    truth is, you dont just diute the sample with acetone. youre also diluting the acetone with the sample. if the sample itself does not have any methanol or toluene in it, the peaks you get are smaller by default.

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