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Bases for measurement | 6
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6.1.7 Care and maintenance
NOTE
The GAK 1400 working and calibration set includes all necessary products for calibra-
tion, care and maintenance of the electrode. Normal cleaning takes place with the
GRL 100 pepsin cleaning solution into which the electrode is immersed for 5 minutes
before being rinsed off with clean water.
NOTE
Crystallisation of the 3 mol/l KCL solution is unavoidable. Crystallised potassium chlor-
ide on the protective cap and shaft can easily be removed with a fingernail or cloth
and is therefore not a defect or grounds for complaint.
Dirty electrodes must be cleaned. The suitable cleaning agents for the pH glass mem-
brane are listed in the table below.
Impurities
Cleaners
General residue
Mild detergent
Inorganic coatings
Commercially available liquid glass clean-
ers
Metal compounds
1 mol/l HCl solution or GRL 100 pepsin
cleaning solution
Oil and grease
Special cleaner or solvent
Biological coatings with protein
1% pepsin enzyme in 0.1 molar GRL 100
HCl solution
Resin lignins
Acetone
Extremely resistant residues
Hydrogen peroxide or sodium hypochlor-
ide
The material of the pH probe must always be protected. Plastic shafts must not be
cleaned in solvents, etc. If in doubt, contact the manufacturer to inquire about suitable
cleaners for the existing electrode. This is also important in the case of aggressive
substances or other substances that are not primarily water-based!
6.2 Redox measurement
6.2.1 Explanation
The Redox potential
0RP
specifies the extent to which the measured sample has an
oxidising or reducing effect relative to the standard hydrogen electrode.
This potential is frequently used in swimming pools as a measured variable for the dis-
infecting effect of a chlorination. For aquaria, the Redox value is also an important
parameter, because fish can only live within a specific Redox range. The measure-
ment is also important in drinking water preparation, waste water monitoring and in in-
dustrial applications.
Measurement takes place relative to the widespread silver/silver-chloride system with
3 mol/l KCL electrolyte. The measurements can be read directly (mV setting) or auto-
matically with the mV
H
unit setting and temperature compensation is calculated based
on the standard hydrogen electrode reference system.
Calibration comparable to the pH measurement does not take place for the Redox
measurement. However, the suitability of the electrodes can always be checked with
Redox testing solutions, such as GRP 100.
