107
Dissolved Oxygen Transmitter
GB Oxix Manual 1209
FW: 841013-009, 846001-002, 841513-009
Guide to Oxygen-free Solution for Checking Oxix D.O. Sensor
Zero Point
Method
• Clean Oxix
®
and its optical window thoroughly.
• Dissolve 3 tablespoons Na2SO3 in 4 litres of tap water in an open con-
tainer (bucket).
• Stir for about 1 minute.
• Immerse the sensor and let it rest in the solution for at least 30 minutes.
(Towards the bottom with the window down; check that there are no air
bubbles on the lens.
Notes
This solution actually contains a concentration of approximately 0.10 ppm
dissolved oxygen. In time, if the solution is left alone, stratification will occur
so that the concentration will be higher towards to the surface.
If you need a reference sample with a dissolved oxygen concentration close to
zero (approx. 0.02 ppm), the reference sample must be made with demineral-
ised water and the solution must rest for 12-24 hours before measuring it.
It is important that the sensor and the optical window are completely clean
when zero-point or calibration is conducted.
How it works
Na
2
SO
3
(sodium sulphite) removes oxygen from the solution since Na
2
SO
3
is
oxidized by O
2
(oxygen) into Na
2
SO
4
(sodium sulphate) following the reaction:
2Na
2
SO
3
+O
2
2 Na
2
SO
4
Materials
• Bucket
• Measuring jug
• Tablespoon
Chemicals/Reagents
Sodium sulphite, Na2SO3, CAS-Nr. 7757-83-7
(Supplier VWR, Bie & Berntsen)
Tap water (alternatively, demineralised water)
Safety Precautions
Safety instructions for Na
2
SO
3
: None. There are no R- or S-phrases for the
product.
