How can i extrapolate and find/show values on a calibration curve

  • Thread starter Thread starter Heekla
  • Start date Start date
H

Heekla

Im am writing the scientific report where I have a calibration curve. I want
to use that and find the concentration of an unknown sample. This is easily
done by hand, but how do i show it on exel and on the chart itself?
 
I will assume that the calibration curve is linear (y = mx + b)
In some cell (say D1) we can find the slope (m) with the formula
=SLOPE(y-values, x-values)
Something like =SLOPE(B2:B12, A2:A12)
Likewise in say D2 we can find intercept (b) with =INTERCEPT(y-values,
x-values)

Let D3 contain the measured y-value from which you need to compute its
x-value
Let these values be Y and X
So Y =mX + b or X = (Y-b)/m
Turning this into Excel: in cell D4 enter =(D3-D2)/D1

Now having done that, you need to be able to report also your confidence
intervals
See
http://people.stfx.ca/bliengme/ExcelTips/RegressionAnalysisConfidence3.htm

By the way: I hope you are INTERPOLATING for the calibration curve not
EXTRAPOLATING
The former is generally valid, while the later is fraught with dangers

best wishes
 
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