Redox potential measurements

Electrodes were calibrated daily in saturated quinhydrone buffer solutions (pH 4 and pH 7) with known redox potentials following manufacturer's instructions (see page 13 https://www.unisense.com/files/PDF/Manualer/Redox%20Sensor%20Manual.pdf). 
A fresh fecal pellet was collected from an individual mouse and then placed on an agar plate. 
The Ag/AgCl reference electrode was positioned to be in contact with the fecal pellet. 
Using a micromanipulator, the redox electrode was lowered and inserted into the pellet. The redox electrode used was a RD-500 glass electrode (Unisense, Aarhus Denmark). 
Data were collected continuously for 3 minutes then the electrode was retracted out of the fecal pellet. Data presented were the average of the 3 minutes of data. 
The electrode was rinsed with DI water between samples. 
At the end of data collection, sensors were cleaned with nitric acid (1:1 H2O) following manufacturer's instructions (see page 21 https://www.unisense.com/files/PDF/Manualer/Redox%20Sensor%20Manual.pdf).