Quadratic Calibration Curve

I created a quadratic calibration curve with 5 standards ranging from 0.001 to 0.06%. The R2 is 0.995. If I run a check standard at 0.02%, the curve calculates the concentration as 0.017% which is good for my application. If I run a check standard at 0.1% (above my curve), Empower3 does not return a result. I've tried several curve weightings but still no result. If I change the curve type to linear, Empower3 gives a result. I'm not that familiar with quadratic curves. Does the unknown concentration have to fall within the curve standard concentrations for a quadratic fit? Can Empower extrapolate if using a quadratic curve?

Best Answers

  • Accepted Answer
    Yes will only report an x value (y=Ax2+Bx+C) within the range of the calibration curve 

  • Accepted Answer
    If you are in a jam, you might be able to switch the calibration to log-log linear so that you can calculate values outside of your curve. The log-log fit should be okay. 

    I had this issue with ELSD methods (company states we must use a quadratic fit for ELSD curves) and both my high and low spike just happened to fall just above and just below my high and low standards in terms of raw area counts. 

    So... I changed the curve type for accuracy only so that I could generate results without having to repeat the analysis all the while stacking the deck in my favor (over deliver spike on low end and under deliver spike on high end). 


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