YSI 85 - Manual (Page 35)

Discussion of Measurement Errors Section 11
YSI, Incorporated Model 85 31
11.3 DISSOLVED OXYGEN PROBE PRECAUTIONS
1. Membrane life depends on usage. Membranes will last a long time if installed properly and
treated with care. Erratic readings are a result of loose, wrinkled, damaged, or fouled
membranes, or from large (more than 1/8" diameter) bubbles in the electrolyte reservoir. If
erratic readings or evidence of membrane damage occurs, you should replace the membrane and
the KCl solution. The average replacement interval is two to four weeks.
2. If the membrane is coated with oxygen consuming (e.g. bacteria) or oxygen evolving organisms
(e.g. algae), erroneous readings may occur.
3. Chlorine, sulfur dioxide, nitric oxide, and nitrous oxide can affect readings by behaving like
oxygen at the probe. If you suspect erroneous readings, it may be necessary to determine if these
gases are the cause.
4. Avoid any environment that contains substances that may attack the probe materials. Some of
these substances are concentrated acids, caustics, and strong solvents. The probe materials that
come in contact with the sample include FEP Teflon, stainless steel, epoxy, polyetherimide and
the polyurethane cable covering.
5. For correct probe operation, the gold cathode must always be bright. If it is tarnished (which can
result from contact with certain gases) or plated with silver, the gold surface must be restored. To
restore the cathode, you may either return the instrument to the factory or clean it using the YSI
5238 probe reconditioning kit. Never use chemicals or abrasives not supplied with this kit.
NOTE: Model 85 probes built before July, 1996 (serial numbers starting with 96F or lower),
should be cleaned with the sanding disc mounted on a FLAT surface. Do NOT use the
curved tool provided in the 5238 probe reconditioning kit on these probes.
6. It is also possible for the silver anode to become contaminated, which will prevent successful
calibration. To clean the anode, remove the membrane and soak the probe overnight in 3%
ammonium hydroxide. Next, rinse the sensor tip with deionized water, add new KCl solution,
and install a new membrane. Turn the instrument on and allow the system to stabilize for at least
30 minutes. If, after several hours, you are still unable to calibrate, return the YSI Model 85
system to an authorized service center for service.
7. To keep the electrolyte from drying out, store the probe in the calibration chamber with the small
piece of sponge.