Say I need to state the uncertainty of my pH measurement in a +/- # [pH unit] format.
The pH-meter calibration result is in the format of %ideal slope. E.g., a commonly used criterion is that the slope (in pH/mV or is it the other way round?...) should be 95-105% of the ideal slope.
How can I use the constraint I have on the measurement error ("pH uncertainty must be within ....) to set appropriate acceptance criteria in my routine pH meter calibration?
Thanks!
Hello, look for calculation of uncertainty of regression line in google.
Good luck!
Rather you could say +/- 0.01 which is the usual error in a pH meter. I think it would be enough for regular analysis
Dear Yonatan,
Your question would be justified if the pH measurement result is really calculated using the theoretical slope factor. Then a deviation of the actual slope from theoretical one, which is expressed as a percentage ideal slope, would lead to an error. However, it is the slope factor found experimentally (from the two-point or multi-point calibration) which is used in actual measurements. The percentage ideal slope displayed on the pH meter is only some kind of performance characteristic of the electrode which tells us about his condition, age, and so on, but this is unrelated to the uncertainty of the measurement unless the one-point calibration is employed, of course.
Regards,
Rouvim Kadis
Thanks a lot!
So it is implied in your answer, Rouvim Kadis , that in order to estimate the accuracy, I must measure another pH standard, AFTER finishing the 2-3 point calibration, and see how far the result is from the nominal value. Right?...
Regrads,
Yonatan
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