I have also been looking ...
Published by Rowan McDonald, Director at ECA Technologies
I have also been looking for something as an alternative to my disastrous experiences with on-line ISE electrodes. Take a look at https://www.ott.com/product-guide-ott-econ-low-maintenance-uv-nitrate-in-situ-sensor/ and https://realtechwater.com/products/uv-vis-sensors/nl-series/ which use UV absorbtion measurement for readings. I like the idea of low maintenance and no calibration.