Xylem ISE Electrodes Na - Manual

Instruction manual for the
SCHOTT ® Instruments
electrodes for measuring
the Na
+
concentration
Preparation and general
If there is an irrigation cap over the sensor and diaphragm,
this should be removed. It contains irrigation fluid (sodium
chlorid solution 0.1 mol/l). The electrode is ready to perform
a measurement. Electrodes stored dry must be irrigated for
24 hours in irrigation fluid. Lacking electrolyt solution 3 M
potassium chlorid solution (L 3008) should be refilled. The
filling level of the electrode solution should always be at
least 5 cm above the level of the measurement solution.
Attention!
Electrolyte solution and irrigation fluid are different.
The closure of the refilling hole must be opened during
measurement. The membrane and diaphragm must be
immersed in the measurement solution.
Please also note the instruction manual of the measuring
device.
For calibration following standard solutions are needed:
0.1 M NaCl
Dissolve 5.85 g sodium chloride in approximately 800 ml
distilled water and fill it up to 1 l.
0.001 M NaCl
Dilute 10 ml of the 0.1 M NaCl solution up to 1 l with distilled
water.
Calibration
The pNa electrode should be connected to the pH-meter like
a pH electrode. Switch the pH-meter in the mV range. For
calibration begin with the lowest concentration and without
rinsing the next solution is measured. The resulting mV
value is noted and a calibration curve printed. The pNa
electrode follows the Nernst equation. The temperature of
the solution must be taken into account.
Example calibration curve
Measurement
The measured solution should be slightly alcalic, but at least
have a pH of 6. Is this not the case, the pH can be adjusted
with sodium free bases like ammonia water or
triethanolamine.
Attention!
Do not take sodium hydroxide solution for adjusting the pH.
The response of the pNa electrode is slow. For a stable
signal it takes from 10-40 min. A shorter waiting time can be
reached when the electrode is rinsed before measuring with
the new solution or an alcalic buffer solution is added.
Cleaning
Dirt and contamination on the sensor and diaphragm lead to
measurement inaccuracies. They can be removed with the
following procedure:
• Coatings and deposits can be removed with diluted
mineral acids (e.g. diss. hydrochloric acid)
• Organic contaminations with the aid of suitable solvents
• Grease with tensid solution or alcohol
• Proteins with hydrochloric pepsine solution (cleaning
solution L 510).
During maintenance there is to pay attention to:
• After cleaning, rinse off the electrodes with distilled water,
do not rub dry.
• Platinum diaphragms must not be treated by any
mechanical treatment. Rinsing (e.g. vacuuming) may be
followed by chemical cleaning (e.g. with diluted
hydrochloric acid).
• The glass membrane can be cleaned by rubbing off with a
fluff-free cloth soaked in ethanol.
SI Analytics GmbH
Hattenbergstrasse 10
55122 Mainz
Germany
Telefon +49 (0) 6131/66 5119
Telefax +49 (0) 6131/66 5001
e-mail: [email protected]
www.si-analytics.com
electrode plug
refilling hole
diaphragm
sensor
P 1
P 2
mV1
mV2
log a
1
log a 2
mV
log a
®