Introduction
I got an Ion Selective Electrode (ISE) from Aliexpress.
More advanced version available from e.g. Pasco scientific, Mettler Toledo and Thermo Fisher.
The simple NO3 ISE
Bante-instruments
The series of ISE’s offered from Aliexpress are from Shanghai INESA Scientific Instrument Co., Ltd (REX?), including the PNO3-1-01 sensor. The webpage of INESA/REX does not contain any more specification on the sensor.
However, the company BANTE instruments sell the same type of NO3- ISE sensor and also offer a suite of manuals for ISEs. The manual for the NO3- ISE
For calibration a solution of NaNO3 (sodium nitrate)
Resources
Thermo Fisher User Guide Ion Selective Electrode
Pasco Scientific Manual and Experiment Guide Nitrate Ion Selective Electrode