area and height difference

Hello!

Why do I have a different areas and height of the peaks of the internal standard, when I add the same amount to each vial? I face this problem both with the calibration and common samples.

I also tried to do four identical vials and they differ as well! Why is that? 

How the calibration curve can be good (r=0.99975) if my internal standard differs so much?

I have GC 8860 and HS 7697A  and I work with quite volatile compounds (Lets assume that there is no mistake in pipetting and/or samples preparation).

Thank you for help!

  • Hi

    Leak may be reason..Check leak first.

    How old is column?

  • Ok.

    Earlier it was working fine with same method & standard???

    Check inlet..

    If it's contaminted then possible.

    2nd thing run any other method with solvent to see that it's instrument problem or dilution or method.

  • By what percentage are they different? That's really the point of internal standards, to account for varying amounts in each run so you do get a good calibration curve.

  • We just began with this method and it was working quite well, but on the other side we just have a few trials. And it is the only one we have right now.

  • I try to do the leak test, but I cannot find the "diagonstick" option :(

  • Above is leak test procedure of 7697a headspace...

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