We have collection oxygen consumption measurements using PreSens spot sensors in the PreSens Sensor Dish system and ran a 12 Milli-Q blanks. In this system you can continuously monitor the oxygen concentration over time in a single vial and calculate the change and rate for each vial. We wanted to calculate the "Method Detection Limit" using the rates and changes found for the blanks to know what change is not distinguishable from background noise. However, I noticed at the beginning of the EPA document (link below) it noted the method detection limit is not applicable to certain measurements such as biochemical oxygen demand. I was wondering what their reason is?

https://www.epa.gov/sites/default/files/2016-12/documents/mdl-procedure_rev2_12-13-2016.pdf