Laboratory Electrodes - Windaus

Tips and information
for successful measurements
Storage
Redox sensors and pH sensors should be
kept in the solution with which the reference
electrode is also refilled (submerge up to the
diaphragm). In most cases, this is KCl solution
(3 mol/l, type no. L 300). Low-maintenance
electrodes are also kept in KCl solution.
Conductivity measuring cells, after
being cleaned and rinsed-off with distilled
water, can be stored in a dry location.
Measuring
With refillable pH sensors and redox sensors,
the refilling opening must be opened in
order to carry out the measurement. The
sensor is then submerged in the measuring
medium at least up to the diaphragm.
With refillable sensors, it is important to pay
attention to the filling level of the electrolyte
solution (see Refilling). Between measurements,
the sensor should be rinsedoff
with distilled water but not wiped off.
Excess droplets can be carefully sponged-off.
Calibrating
Since the measuring characteristics of pH
sensors change with time, they must be calibrated
at regular intervals using appropriate
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buffer solutions. If buffer solutions from bottles
are used, the bottles must be closed immediately
after use. The buffer solution used
should never be put back into the bottle but
must be discarded instead. If very accurate
calibration is necessary, we recommend
DIN single use ampoules that always contain
fresh high precision solutions. Redox sensors
are not calibrated. Their proper function
can be checked using the appropriate test
solutions. For conductivity measuring cells,
the cell constant should be checked and
adjusted at regular intervals with test solutions.
Greater variations in the cell constants
are an indication of soiling or damage.
Refilling
Refillable pH sensors and redox sensors are
refilled with electrolyte solution so that the
filling level of the electrolyte solution is at
least 5 cm above the level of the measuring
medium. With BlueLine electrodes, the easi-
est way to carry out the refilling operation
is to pump the electrolyte solution into the
electrodes using a small dispensing bottle.
Cleaning
A soiled reference electrode should be emptied,
rinsed with electrolyte solution and
then filled again with electrolyte solution.
In case of soiling of the glass membrane or
diaphragm, it should be cleaned in order to
maintain the measuring function. Depending
on the degree of soiling, only the glass
membrane or the glass membrane with
the diaphragm is submerged in the cleaning
solution. Cleaning agents that may have
penetrated into the electrode must not be
allowed to get into the reference system; if
required, the reference electrode must be
rinsed-off with distilled water and electrolyte
solution. Depending on the degree of soiling,
the methods mentioned below are recommended.
After being cleaned, the sensor should be
rinsed-off with distilled water, conditioned
in electrolyte solution for 1 hour or longer
and then recalibrated prior to performing
any further measurements.
Soiling Treatment Info
inorganic adhering substances several minutes, e.g. with HCl improved cleaning action with
0.1 mol/l or NaOH 0.1 mol/l warm solutions (40–50 °C)
organic substances (oil, grease, etc.) rinse off with suitable organic solvent for plastic shaft electrodes, take chemical
(e.g.ethanol) or tenside solution resistance into account. Sensor can also be
wiped of with a soft, moistened cloth.
proteins approx. 1 hour with pepsin/HCl solution
(type no. L 510)
sulphides (on ceramic diaphragm) with thiourea/HCl solution cause: reaction of electrolyte with
(7.5 % in HCl 0.1 mol/l) up to discoloration measuring solution.
remedy: electrodes with platinum
diaphragm and Ag + -free electrolyte
Sensors for all applications
Many different application conditions require the use of appropriate, specifically designed pH sensors.
For your application, you can select the electrode with the optimal pH glass and diaphragm.
pH glasses
Schott electrodes are manufactured with various pH glasses.
These have been optimised for your application and offer a
high degree of measuring accuracy and reliability. Select the
pH glass for your application:
pH glass
N-glass: for general applications across the whole pH range
A-glass: with short response time in drinking water, service
water and waste water; for general application and
in media with low ion content
L-glass: for low temperatures and general applications
H-glass: for high temperatures, in acid and alkaline range,
even with high sodium-ion concentrations
S-glass: in hot alkaline media with good reproducibility and
short response time
Diaphragm
An important factor for a reliable and reproducible pH measurement
is the selection of an electrode with a suitable
diaphragm:
Diaphragm
Platinum diaphragm: universal, shows its strength especially
with solutions containing
solids and at extreme pH values and
temperatures. It is ideal for titrations
and very insensitive to stirring.
Ceramic diaphragm: robust for general applications, low
electrolyte outflow rate.
Ground joint preferred for liquids with high solids
diaphragm: contents, easy to clean.
Fibre diaphragm: for robust, minimum-maintenance
electrodes. Preferred for general
applications and field measurments.
KPG ® annular gap on minimum-maintenance
diaphragm: electrodes, with symmetric annular
gap, insensitive to soiling.
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