or kimwipe afterwards; rinse off the electrode with distilled water, then shake off excess
water; Add some new inner solution into the membrane cap; screw on the cap. Then perform
the saturated oxygen calibation according to 4.2 before measuring again.
4.5.4 Replace the membrane cap
When the DO electrode’s response time becomes slower, obvious errors occur in
measurement, or when the sensitive membrane of DO electrode is wrinkled, cracked or
damaged at any extent (the well-functioning membrane surface should look perfectly
smooth), it’s time to replace a new membrane cap (DO503) according to the following steps.
a) Screw off the membrane cap;
b) Rinse off the electrode without membrane cap with distilled water and shake off
excess water.
c) Clean on the cathode surface (gold slice) with a clean tissue or kimwipe;
d) Add new inner solution (DO502) into a new membrane cap (DO503) slowly and do
not let any air bubbles appear. If you found any air bubbles in the cap, carefully flick
on the membrane cap to eliminate them.
e) Place the membrane cap on the table and put in the electrode vertically, slowly twist
in, and then screw on the cap tightly. The excess inner solution will be squeezed out.
Please wipe it off with tissue and rinse off the electrode in distilled water.
f) Check if there are any air bubbles in electrolyte (except for the smaller air bubbles),
If so, re-assembly is needed.
g) Do not touch the sensitive membrane with fingers directly because the sweat and
grease will affect the quality of the membrane.
4.6 Zero Oxygen Calibration
Usually there is no need to do zero oxygen calibration unless you have a high requirement
for accuracy in low oxygen level (<1.0 ppm). To do zero oxygen calibration, follow the steps
below:
Prepare 100mL of zero-oxygen water: In a 100 mL beaker, add in 5.0 g anhydrous sodium
sulfite (Na
2
SO
3
); add 100 mL distilled water; mix well to dissolve. Not that the zero-oxygen
water is only effective within 24 hours.
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