H33.0.02.6C-09
Operating Manual GMH 3530
page 11 of 14
Slope is too high
- Electrode defective
- Buffer solution defective
replace electrode
use new buffer solution
Incorrect calibration temperature
calibration can only be done at 0..60°C
13 The pH-electrode
pH-electrodes are wear parts which need to be replaced, depending on the chemical or mechanical stress they are
subjected to, if the values required can no longer be kept even after thorough cleaning and recovery. Please take
into account that there are several materials which attack glass when they are in water solutions; other chemicals
may react with the KCl-solution in the electrode thus causing blockings in the diaphragm.
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
Problems may also occur when taking measurements in low-ion media containing solvent. Some of the problems
occurring when taking measurements in such media can be counteracted by using a double-chamber electrode
(Type GE 103)
with suitable bridging electrolyte (type depending on application).
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.
13.1 Various applications require special electrodes
1.
Measurements in low-ion media
(rain water, aquarium water, VE-waters)
Type GE 104 (special facetted electrode as of 50µS/cm) or GE 106 (as of 100µS/cm)
.
2.
Sea water aquariums
Standard pH combined electrodes with 3mol KCl
(type GE 100)
.
3.
Photographic laboratories
Use double-chamber electrodes, with bridging electrolyte (1 molar potassium-nitrate solution); potassium-nitrate
solution has to be exchanged if necessary, make sure to fill water cap for storage of electrode with potassium-
nitrate solution
(type GE 103)
.
4.
Pools
Standard pH-electrode with 3mol KCl
(type GE 100 )
.
5.
Soil checks
Glass electrode with several diaphragms
(type GE 101)
. Use insertion mandrel!
6.
Cheese, fruit, meat
Insertion electrode
(type GE 101).
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 main-
tained 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.
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