2 point calibration formula

From German brewing and more
Jump to: navigation, search

When the pH meter doesn’t calibrate anymore or is only capable of a single point calibration, the following formula can be used to calculate the pH from the measurements of calibration buffer solutions

pHx = pHref1 + (pHref2 – pHref1) * (Mx – Mref1) / (Mref2 - Mref1)

  • pHx - the pH of the sample
  • pHref1 - the pH of the calibration buffer 1 (generally 4)
  • pHref2 - the pH of the calibration buffer 2 (generally 7)
  • Mref1 - the measured value for buffer 1
  • Mref2 - the measured value for buffer 2
  • Mx - the measured value for the sample

When using 4 and 7 pH buffer solutions, the equation simplifies to

pHx = 4 + 3 * (Mx – M4) / (M7 - M4)

But most pH meters will do this automatically and such complicated calculation is not necessary.