Why would the readings on the LDO® probe be significantly higher than a membrane-style DO probe?

Document ID

Document ID TE422

Version

Version 2.0

Status

Status Published

Published Date

Published Date 27/05/2017
Question
Why would the readings on the LDO® probe be significantly higher than a membrane-style DO probe?
Summary
Dissolved oxygen reading using the LDO® probe is significantly higher than the reading from a SensIon meter
Answer
This is generally seen at dissolved oxygen concentrations greater than 5 mg/L. The reasons for this difference are complex, but are due to lower than actual readings from traditional probes that use gas-permeable membranes. Membrane probes consume oxygen at the electrode surface, and therefore oxygen from the sample must continually go through the membrane to replenish the oxygen consumed. This is why stirring is important with this type of probe. The more oxygen in the sample, the more oxygen must go through the membrane. At high concentrations (greater than 5 mg/L O2), these probes consume more oxygen than can be transported through the membrane, resulting in a depletion at the electrode surface. In contrast, the LDO® probe does not have a membrane and does not consume oxygen. An equilibrium between oxygen in the sample and oxygen in the sensor film on the sensor cap is easily maintained, and does not require stirring.