BUCHI KjelSampler K-377 - Manual (Page 139)

7 Maintenance
139 K-375/376/377 Operation Manual, Version B
7 .7 .2 Cleaning the pH electrode
If the glass membrane or diaphragm are dirty, clean them to maintain the measuring function.
Depending on the degree of contamination, submerge only the glass membrane or the glass
membrane with the diaphragm into the cleaning solution.
Depending on the degree of contamination, the methods mentioned below are recommended.
After cleaning, rinse off the electrode with distilled water, condition it in electrolyte solution for 1 hour
or longer and recalibrate it prior to any further measurements.
Table 7-1: Cleaning methods of the pH electrode
Soiling Treatment Comments
Inorganic substances Several minutes, e. g. with
HCl 0.1 mol/L or NaOH 0.1 mol/L Improved cleaning action with warm
solutions (40–50 °C)
Organic substances
(oil, grease, etc.) Rinse off with a suitable organic
solvent (e.g. ethanol) or tenside
solution For plastic shaft electrodes, take
chemical resistance into account.
Sensor can also be wiped off with a
soft, moistened cloth.
Proteins Approx. 1 hour with pepsin/HCl
solution 5% pepsin in 0.1 mol/L HCl
Sulfides (on ceramic
diaphragm) With thiourea/HCl solution (6.5 % in
HCl 0.1 mol/L ) up to discoloration Cause: Reaction of electrolyte with
measuring solution.
7 .7 .3 Replacing the buret
As a rule, the need for replacing the buret occurs only rarely. It has to be replaced only as a result of
a defect.
7 .7 .4 Cleaning the splash protector and the rubber seal
In case the splash protector or the rubber seal is contaminated and this contamination was not
removed during the daily maintenance work, proceed as follows:
• Dismount the splash protector and remove the rubber seal.
• Rinse the splash protector with water to remove sample residues.
We recommend to replace the glass splash protector after approximately 3000 – 5000 determi-
nations, depending on the kind of application and frequency of maintenance. The plastic splash
protector can last more than 8000 distillations.
To prolong the lifetime of the seal, rinse it with water, especially if working with crystalline products.
Afterwards, dry it with a soft cloth, remount it and put the splash protector back in place.