15
4 Calibrating a pH combination electrode
The parameters of pH combination electrodes are subject to large variations
due to age and individual variations.
It is therefore advisable to check the calibration of combination electrodes
before making measurements. If the deviation is outside the permissible
tolerance, then the combination electrode must be recalibrated.
Calibration requires buffer solutions that have a precise pH value.
A buffer solution from the
-
standard series
(4.00 pH, 7.00 pH) JUMO standard buffer solutions
-
DIN series
(1.68 pH (A), 4.01 pH (C), 6.87 pH (D), 9.18 pH (F)
and 12.45 pH (G))
-
or any other buffer
(neutral buffer in the range 6.5 to 7.5 pH)
can be used.
4.1
Preparation
✱
Select the measurement function “pH”, see Chapter 3.1 “Select
measurement function: pH/redox mV/redox mV
✱
Activate 2- or 3-point calibration (2-point calibration is standard), see
Chapter 3.2 “Select 2- or 3-point calibration (only for pH measurement)”,
page 11.
✱
Carefully remove the protective cap from the pH combination electrode (the
protective cap contains 3-mol KCl).
✱
Rinse the combination electrode and the temperature sensor (if present)
with de-ionized (distilled) water and dry off.
Buffer solutions have a limited usable life that is, for instance, seriously
reduced by inadequate rinsing and drying of the combination electrode when
changing solutions. This can lead to calibration errors! Use the freshest
possible solutions for calibration. Rinse with de-ionized or distilled water!
Automatic temperature compensation during calibration
The signal from the pH combination electrode and the pH buffer are both
temperature-dependent. A Pt100 temperature sensor (option) connected to the
hand-held meter will automatically compensate for temperature effects.
If a temperature sensor is not available, then the actual temperature of the
buffer that is being used should be entered as accurately as possible, see
Chapter 3.7 “Manual temperature setting for operation without a temperature
sensor”, page 13.
If the standard buffer series or the DIN buffer series is used, then the
temperature effects on the buffer will also be compensated.
If manual buffers are chosen, then the pH value of the buffer at the present
temperature must be entered.