Conditions associated with drift or erratic readings while using a pH meter:
(1) air bubbles in the electrode
(2) trying to measure the pH of a liquid with a very low ionic strength
(3) incompatibility between the choice of the electrode and the application
(4) contaminants, including a clogged or dirty junction
(5) improper conditioning (either initially or after storage)
(6) problems in the electronics including a damaged wire
(7) significant temperature difference between the electrode and sample
(8) using plastic ware and a magnetic stirrer
Causes of "pseudo" drift (equilibrium takes longer to be achieved and the change in readings prior to equilibrium interpreted as drift):
(1) large sample volumes
(2) use of a gel-filled or plastic electrode
With pseudo-drift the readings should be stable once the system has equilibrated.
