I have got an equation of calibration using SDDC method of arsenic determination:
y = 0.000x - 0.024 ( R² = 0.970)
I have tried to both include/omit the blank values but everytime I do, the slope is zero though visually the line is inclined towards x axis by say 30 degrees.
X-axis: concentration of arsenic
Y-axis: absorbance value
Concentration: 0 , 28.57, 57.14, 142.85, 285.71, 428.5, 571.42 ppb in Y axis
Absorbance : 0.006 0.019 0.053 0.123 0.265 0.43 0.589
o
Please see the attached
The fit looks ok to me. A simple linear fit (y=mx+c) gives a intercept of -0.01 which could be due to baseline error. The slope is 0.001
You should force the intercept to 0. Fit y=mx and not y=mx+c. You also need to subtract the OD value at 0 ppb As from all the OD values.
The slope is indeed very close to 0. For a visual interpretation of that you need to set the same minimum and maximum values for both the x and y axis. See the attached file.
Thanks Tuhin, but did you plot in excel?
I did with Excel 2016 & got that equation.
Sorry Tuhin, I sent the wrong file. The equation that I mentioned in my question was calibrated 12 days ago. The file presently sent has been done just 3-4 days ago. Anyway, I worked in the lab & got that equation whereas in my laptop after downloading the file, the equation is different!
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