pH Circuit Design Help Needed

I was handed a project to correct a pH circuit design. I have the circuit breadboarded and running.

The problem with the circuit is it is extremely slow to resond to changes in pH, on the order of 10 minutes to go from a pH reading of 7 to 10 (2v to 4.5 v on the op amp output)

The problem with me is that I am not an electronics engineer and do not understand why the circuit has such a slow response.

Can someone please explain to me why the responce rate is so slow and more importantly how do I correct it?

thanks

I can practically guarantee you that the 1uF cap on pin 3 of the op amp is the cause of your problem. Remove it and try your test again. Then, for noise rejection, make the cap as large as you can without slowing down response too much. **broken link removed** is a discussion of a pH meter circuit. If your circuit doesn't have it, you should consider how to do temperature compensation. The schematic I referenced has one solution.

You are correct sir. I pulled the 1uf cap and put in a .01uf, works like a champ now. Thanks for your help.