area and height difference


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!

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