9
CALIBRATION / ELECTRODE COMPENSATION-pH
WHEN CALIBRATION IS REQUIRED
1. Upon first use of instrument
2. After changing batteries or AC power failure
3. When changing pH electrodes
4. When pH electrode fails to properly measure known buffer
5. Using an electrode that has not been used for a period of time
MATERIALS REQUIRED FOR CALIBRAT ION
1. Actual electrode to be calibrated
2. Buffer solutions 4, 7, and 10
3. Distilled water for rinsing electrode
4. Celsius thermometer or ATC electrode
5. Four clean beakers or other suitable containers
TECHNICAL THEORY REGARDING “CALIBRATION”
While the following adjustments are made upon the instrument itself, the actual
process involves compensating the meter’s sensitivity and software algorithm for
the present status of the specific electrode to be used. Therefore, whenever you
change electrodes, you must re-calibrate. pH electrodes deteriorate with use and
with time, therefore they should be verified using known fresh buffer solutions
before important sample measurements are made. The following process is a two
point calibration which enters the electrode’s offset and slope into memory.
Setting of the offset is done at pH 7 (called STAND throughout this manual);
while the slope is set at either pH 4.01 or 10.01 (called SLOPE in this manual).
Choose the slope buffer according to whether your sample measurements are more
likely to be acidic (4.01) or alkaline (10.01).
Buffer solutions, especially alkahne buffers, are subject to absorbtion of CO2from
the air. They should be stored in tightly sealed glass containers when not in use
and replaced frequently.
