method:
1. Quasi-sum curve:
Enter the first line: Â Â Â Concentration value, Â Â Â Â Â Â Â Â Â Â Â Â Such as 0 10 50 100 400
Enter the second line: the adjusted od value at this concentration , such as 0 0.586 1.397 1.997 3.42
Select the data of these inputs, use the chart button in the insert, enter the chart wizard, select " xy scatter plot" in "Standard type "; select "polyline scatter plot" in "Sub-chart type", press "Next "Select "Series generated in the line", press "Next"; data mark can be filled in: such as data y- axis, OD value; data x- axis, concentration; press Next, click Finish. Available curve.
Click the curve, right click, select "Add Trendline", in the type, select the polynomial; in the option, select Show Formula, select Show R Squared Value.
Get the formula and the R- squared value.
You can also use the method described above: Â Double-click on the chart and enter it into the data in the chart to fit the curve.
2 , calculate the concentration:
 First experiment:
The standard curve is:
y = -4E-05x2 + 0.026x
R2 = 0.9745
As an example, the OD value is known and the concentration is calculated.
Since y = -4E-05x2 + 0.026x , you can get:
4E-05x2 - 0.026x + y = 0
Ax2 + bx + y = 0
a = 4E-05 ; b = Â - 0.026 ; Â
x =(- b -( b*b - 4ay )(square root)) /(2*a)
Substituting a , b , and y values,
x =( 0.026 -( 0.026*0.026-0.00016*y ) ( square root) ) /(2*0.00004 )
In excel you can use the following formula:
x = (0.026-EXP(LN(0.026*0.026-0.00016*y)/2))/(2*0.00004)
Â
The general formula is:
x =(- b - EXP(LN ( b*b - 4ay ) /2) ) /(2*a)
You can apply excel 's formula copy function to calculate all concentrations
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