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#1
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calibration curve
I am setting up a chemistry calibration curve using data below
OD reading Concentration ..020 0 ..045 10 ..245 40 etc Plotting in XY scatter chart and get trendline using polynomial function. How can I determine the concentration of an unkown solution ? I want to use trendline data to do this. |
#2
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calibration curve
Put the Conc data in column A and the OD data in B
You can have headers ("Concentration", "OD" ) in row 1 Let's say the last row is 10 Select A1:B10, click the chart tool, select XY chart, use the first subtype (markers without line) On chart right click on a data point, select Insert Trendline and specify polynomial or required order To out the coefficients into cell use LINEST as shown in http://www.stfx.ca/people/bliengme/E...Polynomial.htm You now have equation such as y = ax^2 + bx +c where x is conc and y is OD You will have real numbers 12.45 = 2.34c^2 - 5.46c + 8.9 and will need to solve for x Most calibration curve I every used were linear y =mx + b So x = (y - b)/m best wishes -- Bernard V Liengme www.stfx.ca/people/bliengme remove caps from email "PAUL GRAZIDE" wrote in message ... I am setting up a chemistry calibration curve using data below OD reading Concentration .020 0 .045 10 .245 40 etc Plotting in XY scatter chart and get trendline using polynomial function. How can I determine the concentration of an unkown solution ? I want to use trendline data to do this. |
#3
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calibration curve
Are you sure that a polynomial is an appropriate calibration curve here? You
don't give enough points to assess the fit, but I am much more familiar with OD calibration curves that are either log-linear or a 4- or 5-parameter logistic equation. Jerry "PAUL GRAZIDE" wrote: I am setting up a chemistry calibration curve using data below OD reading Concentration ..020 0 ..045 10 ..245 40 etc Plotting in XY scatter chart and get trendline using polynomial function. How can I determine the concentration of an unkown solution ? I want to use trendline data to do this. |
#4
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calibration curve
Polynomial in this case is correct, because the curve is not linear. If
curve was linear, then i would use y=mx+b. Thanks "Jerry W. Lewis" wrote in message ... Are you sure that a polynomial is an appropriate calibration curve here? You don't give enough points to assess the fit, but I am much more familiar with OD calibration curves that are either log-linear or a 4- or 5-parameter logistic equation. Jerry "PAUL GRAZIDE" wrote: I am setting up a chemistry calibration curve using data below OD reading Concentration ..020 0 ..045 10 ..245 40 etc Plotting in XY scatter chart and get trendline using polynomial function. How can I determine the concentration of an unkown solution ? I want to use trendline data to do this. |
#5
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calibration curve
I did not suggest that your data was not curved. I suggested that over an
appropriate range log(OD) might straighten it into a line. Barring that, you would probably get a better fit from a model that flattens out toward max and min values (as OD must) instead of increasing or decreasing without bound (as a polynomial must). Jerry "PAUL GRAZIDE" wrote: Polynomial in this case is correct, because the curve is not linear. If curve was linear, then i would use y=mx+b. Thanks "Jerry W. Lewis" wrote in message ... Are you sure that a polynomial is an appropriate calibration curve here? You don't give enough points to assess the fit, but I am much more familiar with OD calibration curves that are either log-linear or a 4- or 5-parameter logistic equation. Jerry "PAUL GRAZIDE" wrote: I am setting up a chemistry calibration curve using data below OD reading Concentration ..020 0 ..045 10 ..245 40 etc Plotting in XY scatter chart and get trendline using polynomial function. How can I determine the concentration of an unkown solution ? I want to use trendline data to do this. |
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