Amplifier and Ph electrode

I am trying to implement an Alkalinity measurement device.

1. I am using reference electrode[16-702] and ph electrode[16-705] by MicroElectrodes, INC
   1. The output value from electrode will be between range of plus/minus 410 mV
   2. Response time for ph electrode[16-705] is 5 - 15 seconds
      

1. Now we need a amplifier that can take input from electrode will be in range of plus/minus 410 mV.
   1. Also the amplifier needs to be able to take input impedance greater then 1 * 10^12 [1 Tera]
   2. Also the amplifier needs to have bias current under 1 * 10^-12[1 Pico]
   3. The output gain of plus/minus 20 V
2. The output of the amplifier will be input to A/D converter[USB-1408FS]  by Measurement Computing.

At the moment I have ph electrode connected to AD8222 amplifier and something in the system is causing a intereference

which is causing a incorrect output signal or noise in the signal.

Is AD8222 amplifier I am using correct or Should I use some other Amplifier?

Message was edited by: ambar rathie