Any reliable in-line Hydrogen Peroxide measurement system? Not affected by other ions.
What type of AOX system are you working with, UV, Ozone, etc? is it for potable water such that you will be using chlorine for a disinfectant residual at the end of the process?
Do you need the system to be accurate? On a past project we had to dose peroxide at say 20 mg/L and about 70% of that remained after UV so it wasn't critical that the peroxide was dosed accurately. The peroxide residual was quenched via carbon and then dosed with chlorine to reduce the remainder of the peroxide residual . Chlorine was dosed accurately via the available controllers in a PID conrol loop to produce the required residual for the reservoir.
Prominent offers a sensor, but I have no experience with its use. The PEROX sensor mentions no cross sensitivity to chlorine: https://www.prominent.ca/en/Products/Products/Measuring-Control-and-Sensor-Technology/Sensors/p-sensors-hydrogen-peroxyde.html