H70.0.01.6C-02 Operating Manual GMH 3531 page 9 of 18
Examples:
- with solutions containing protein, like they are used on the medical and biological sector, KCI may result in
the denaturation of the protein.
- coagulated varnish
- solutions with a relatively high concentration of silver ions
Any material depositing on the measuring membrane or the diaphragm will influence the measurements and
have to be removed at regular intervals. This can be done by means of automatic cleaning equipment.
Electrodes have to be stored in a way that they are kept wet. An adequate solution is to
store them with suitable protective cap filled with KCl 3 M. Please consider also the
instructions in the electrodes manual!
6.4.3 pH electrode suggestions
Different applications require different electrodes
1. Measurements in low-ion media (rain water, aquarium water, VE-waters)
GE 104 BNC (as of 20 µS/cm)
2. Sea water aquariums
Standard pH electrodes with 3mol KCl (GE 100 BNC, GE 117)
3. Swimming pools
Standard pH electrodes with 3mol KCl (GE 100 BNC, GE 117)
4. Soil checks
Glass electrodes with several diaphragms (GE 101 BNC); use insertion mandrel!
5. Electroplating, some paints and lacquers
Glass electrode GE 151 BNC
6. Cheese, fruit, meat
Insertion electrode (GE 101 BNC or GE 120 BNC).
When taking measurements in cheese, milk and other high-protein products use special cleaning agent to
clean electrode. (pepsin solution - GRL 100).
Standard cleaning: apply 0.1 molar HCl-solution for at least 5 minutes or protein cleaning agent.
The average service life of an electrode is 8 to 10 months but may be increased to 2 years if electrode is well
maintained and treated carefully. We regret not being able to give a more detailed information as this is
highly dependent on the individual case of application.
6.5 Calibration of pH measurement
The electrode data of pH electrodes are subject to fluctuation due to ageing and manufacturing tolerances.
Therefore it is necessary to check the calibration with buffer solutions before measurements take place. If
deviations are too large, a recalibration is necessary. See also chapter 10 GLP.
Buffer solutions are liquids with an accurate pH-value. The following buffers can be used for calibration:
- Technical buffer series PHL (ready to use, pH 4.01, pH 7.00 und pH 10.01)
- Standard series GPH (buffer capsules to be mixed with water pH 4.01, pH 7.00 and pH 10.01)
- DIN series CAL dIn (pH 1.68 (A), pH 4.01 (C), pH 6.87 (D), pH 9.18(F) und pH 12.45(G))
- Arbitrary buffer CAL Edit (neutral buffer ranging from 6.5 ... 7.5pH)
Service life of a buffer solution is limited and will be further reduced unless the electrodes are
properly rinsed and dried when changing over the solutions. This may even result in incorrect
calibration! We recommend to use new buffer solution for calibration, as far as possible, and to
rinse with deionized or distilled water.
6.5.1 How to prepare calibration buffers of standard GPH series (capsules)
See notes B.
6.5.2 Automatic temperature compensation during calibration
Both the signal of the pH-electrode and the pH-buffer are depending on temperature. If a temperature probe
is connected, the temperature influence of the electrode is compensated automatically during measuring as
well as during calibration. Otherwise enter actual buffer temperature as accurate as possible (see below).
When working with the standard or DIN-buffer series, the influences of buffer temperature are also
compensated. If buffers are entered manually, make sure to enter the pH-values of the buffers at the relevant
temperature to ensure optimum calibration of the device.
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