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

Dear Yonatan,

You are right. The accuracy in pH measurement is estimated in this way. It is a common procedure in verification of a pH measuring instrument to check the pH value of a third buffer solution having pH between the two of the calibration buffers. For instance, if standard pH buffer solutions with pH 4.00 and 9.18 are used for calibration, the measurement is made with the buffer 6.86 (25° C). The pH measurement error that is the difference between the measured value and the reference value of that buffer should be less than the maximum permissible error specified for the pH meter of a given type.

Good luck