[sprtfan]

I made a curve with concentrations at 0.05, 0.1, 0.5, 1, 5, 10, 15, 20 ng/ul in ethyl acetate.  I'm running the samples by GCMS.  I'm not sure the best was to describe the results but there is an obvious curve up starting with the 5 ng/ul standard and have an r^2 of 0.92.  If I break the standards up into groups, (0.05-1) and (5-20), I get an r^2 of 0.995 for both. 
I have made the standards 3 separate times and get the exact same results.  I did reuse my 1mg/ml stock solution each time though.  I use the 1 mg/ml stock to make the 5ng-20ng samples and then use the 5 ng sample to make the rest.  I'm using graduated disposable pipettes to make all of the dilutions.  I do not do this very often but have never had much trouble in the past.  I double checked my calculations and they should all be right.  Could the problem be with the ethyl acetate being volatile? Could I just be consistently making an error while making the dilutions?   Thanks for any insight

[Hunter2]

Sometimes you have to use log(c), 1/log(c) and others if the normal values not linear. Which substance are u detecting.

[sprtfan]

Sometimes you have to use log(c), 1/log(c) and others if the normal values not linear. Which substance are u detecting.

Thanks for the reply.  I figured out that the problem was caused by a background ion at a similar mass to the fragment that I was using that was disproportionately increasing the area counts of my lowest calibration points.