Metrolab Blog

PH Electrodes – Basic questions vol1

What is the measuring error of a pH electrode? How accurate is my pH electrode?

The measuring error cannot be determined by looking at the electrode alone, it must be considered as a function of the whole measuring system including the pH meter. There are a number of factors that affect the accuracy of a pH measurement, such as the condition and age of the electrode, the electronics of the instrument, the temperature probe and the accuracy of the calibration, amongst other factors. Across the system we can expect the measuring error of a standard sample under standard conditions to be approximately 0.05 pH units.

It is only possible to determine the accuracy of the measuring system more precisely by empirically measuring it. This can be done by measuring the pH value with the same electrode several times, rinsing regularly in-between measurements. The readings must then be statistically evaluated to express accuracy.

How does one store sensors correctly?

All user manuals come with necessary information about the short and long time storage of the respective probe.

General tips for long time storage:


  • pH and ORP electrodes: with wetting cap filled with reference electrolyte (often 3 mol/L KCl); it is also possible to store the electrode in pH buffer 4 and 0.1 mol/L HCl
  • ion selective electrodes: dry
  • conductivity sensors: dry
  • polarographic DO sensors: with filled electrolyte and green protective cap
  • galvanic DO sensors: with storage vial filled with 10% NaCl