The type of material used as a membrane also critically affects the performance of the system. Some have found that 0.001" to 0.0009" thick polyethylene, which is readily available from normal sandwich bags, works best for O2.

Membranes that are more oxygen permeable, such as TFE Teflon or silicone, may be required for experiments at low temperatures or when a response rate faster than 4 seconds is desired. However, these materials will cause a greater motion artifact because the concentration gradient extends further into the bulk solution. TFE Teflon will also stretch and thin over time, causing the initial amplifier calibration to become incorrect. FEP Teflon usually works well, but is too stiff to wrap around the small electrode tip. Saran type wrap is not sufficiently permeable to oxygen to be useful as a membrane.

The structure of sandwich bags tends to be poor even if the base material is the same.


Regards,
Tom Barr