pH glass electrode input path

[analityk]

Hello,
how to build a reliable and still precise input buffer for pH glass electrode signals?
In my new work i have notice that someone build realy crapy input for this purpose and it need to be changed. I do it in terms of leakage currents etc but input buffer opamp input bias current is lower than 5 pA.
I have try measure voltage from glass pH probe with 10G input impedance multimeter but impedane is way to small to do this measurement.
Anyway end user may touch probe and electrostatic discharge can fired up input opamps. How to properly secure inputh path from esd? Can i use some type of TVS with extremly low leakage currents?
Sincerely

PS:
I have read this papers but definitely not found solution:
https://www.ti.com/product/LMC6482
https://www.ti.com/lit/ds/symlink/opa145.pdf
https://www.mouser.pl/ProductDetail/Texas-Instruments/OPA928DR?qs=2wMNvWM5ZX5RgAZJHoeYSw%3D%3D

[CaptDon]

Maxim and several others make amplifier I.C.'s specifically for PH probe use. We used several and we powered them with 9vdc alkaline batteries. The batteries lasted for nearly their shelf life!! It has been a long time ago but I recall the probes we used came with BNC connectors.

[Faranight]

Back in the days I used an INA116 for this purpose, which is a femtoamp instrumental opamp with included pins for guard rails, but the part has been NRND-ed since. See, if Texas Instruments offers any more up-to-date parts.

[aliarifat794]

Your choice of op-amp with an input bias current below 5 pA is a good start. Op-amps like the LMC6482 or OPA145, are suitable candidates due to their low input bias currents.

[Kleinstein]

There are plenty of low bias OP-amps. It still needs a clean layout and board to avoid extra leakage, especially when the humidity goes up.

For protection a high value (e.g. 470 K - 5 M) series resistor can do most of the protection. Most OP-amps have some internal diodes that are than sufficient. If needed bootstrapped low leakge diodes like BAV199 could be used as additional clamps.