HND-R106
HND-R106 K09/0422
page 27
18. Preparation of ph Buffer Solution
Working and Calibration set HND-Z0763 (see chapter 19.2
Accessories
)
How to prepare a calibrating solution:
-
Fill 2 plastic bottles with 100 ml distilled water (e.g. battery water) each. 100
ml will cover the entire cylindrical area, i.e. approx. 55 mm as of bottle base.
-
Open pH 7 capsule (green) carefully (turn one half of the capsule while pulling
and make sure not to spill any solution); put content (including both capsule
parts) into one of the bottles.
-
Put content of pH 4 capsule (orange) (resp. pH 10), including both capsule
parts, in the second bottle. The capsule shell will colour the liquid with the
respective characteristic colour:
orange = pH 4.0; green = pH 7.0, blue = pH 10.0
Make sure to prepare buffer solutions in time as they can only be used after 3
hours. Shake well before use.
Eventually the capsules won't resolve totally. The residues can stay in the liquid
without any negative effect, or they can be removed after colouring the liquid.
The buffer solutions have a limited operational life of 3 - 4 months and should be
renewed after this period. The capsules itself are practically stable for an
unlimited time and should be kept in reserve.
General maintenance and measuring instructions for pH combi-electrodes:
Make sure to observe the following points to maintain optimum capacity and
accuracy of electrode as long as possible:
-
Important!
Make sure to always keep pH-glass diaphragm in a slightly moist
condition. If electrode is not used, the pH-glass diaphragm has to be immersed
into a 3 mol/l KCl solution for storage.
Drying out of the pH-glass diaphragm will affect both its capacity and sensitivity.
In order to wet it throughout, put glass diaphragm in a 3 mol KC
l
solution for 24
hours.
-
Check liquid level of reference electrolyte at regular intervals; if necessary, top
up with 3 mol/l KCl solution through filling hole using a syringe or pipette.
-
As they will influence the measurements, any deposits that may accumulate on
the measuring membrane or diaphragm have to be removed regularly.
When conducting measurements in cheese, milk and other products containing
proteins, a special cleaning agent HND-Z073 (pepsin solution) has to be used
for cleaning of the electrode.
-
Dirty electrodes have to be cleaned. You will find suitable cleaning agents for the
pH-glass diaphragm in the following table:
