i am measuring(whit 1s interval) a voltage point in a electro-chemical system, via an op amp configured as a buffer(voltage follower) since i need measuring point to have reaaaaaally high impedance, to prevent effecting very sensitive chemical process. I am measuring voltages in range of 20 to 200mV.
I got that part up and running, but the other thing is that while i am not measuring, that same point must be shorted to ground. So i tried that whit a mosfet (p16nf06l), but the problem is that while mosfet in closed state leaked very little current (uA), it is still a LOT comparing it to an op amp that i use(AD8542ARZ1), which has couple of pA and even if i close the mosfet while measuring, the value that i measure is around 40mV, instead of actual 180mV.
So basically i need to find a component or a circuit that will be able to COMPLETELY(or near completely) disconnect the grond from emasuring point while i measure, and then after, when i open it, starts conducting. When in conducting phase it does not mather if it has couple of 10 Ohms, but when it is in non-conductive state, the leake current should be <100pA. And i cant use mechanical realys.
Thanks in advance.