Aanderaa 4330 Operating Manual page 68

It has however been concluded that when sensor foils are new they go through a maturation process that can last for approximately 1 month. The
maturation will lead to lower readings and explain why some of the delivered sensors read some % lower than when they were calibrated.
When you receive the sensor from the factory no calibrations are needed but of course you should check that it is working properly
CCAP6
Q. The brochure says accuracy of 8µM or 5% (whichever is greater).
Does this mean that at very low levels the accuracy is 5% of the measurement?
A: No, this means that the accuracy is 8µM for readings below 160µM and 5% for readings above 160µM. Starting in the first half of 2012 AADI offers a
multipoint factory calibration which give absolute accuracies of ±2 µM or ±1.5 %over the whole range of temperatures and oxygen concentrations.
CCAP7
Q: Is there a minimum measuring point or will the sensor go all the way down to zero?
A: It will go all the way to 0. There is no minimal measuring point. If a calibrated Optode reads a constant low value (e.g. from -1 to 1 µM) when the oxygen
level in reality is 0 it most likely reflects an inaccuracy in the zero point calibration or in the temperature compensation.
CCAP8
Q: When calibrating, which substance should I use to remove the oxygen in the water?
A: At Aanderaa we use Sodium sulphite for this purpose.
Sodium sulphite rapidly removes the oxygen and as long as crystals of the compound can be seen the oxygen level in the water will stay at 0. Sodium
sulphite also has the advantage of being inexpensive and the level of toxicity is low.
There are many other chemical substances that could be used for the same purpose.
Some investigators use Sodiumdithionit, which is also effective but more expensive and more toxic.
Bubbling with gases (e.g. N2, Argon etc) will also "strip off" the oxygen from the water but this takes longer time and sometimes, especially if the water
volume is large, it can be difficult to know when a true zero oxygen level has been reached.
Another way of removing gas/air/oxygen from water is to boil it for at least 15 minutes and let it cool off in a gas tight vial (e.g. of glass). Be careful when
opening the vial, exposure to the air will lead to immediate air contamination.
CCAP9
Q: When calibrating at saturation, which type of device should I use to get 100% saturation?
A: It is advisable to use standard aquarium equipment, which is normally inexpensive.
An aquarium pump connected to a tube which has been fitted with porous stone (bubble dispenser) at the end is suitable.
This will create small air bubbles that are efficient in equilibrating the water rapidly.
page 68 of 93
TD 269 OPERATING MANUAL
OXYGEN OPTODE 4330, 4831, 4835
June 2017