Why is the potential changing in my electrochemical cell setup?

[neuro11]

I took some phosphate buffer saline(7.4) into a beaker, included a Au electrode and reference electrode (Ag/AgCl) and tried to measure the potential using multimeter. The temperature and pressure is assumable same. The multimeter shows the potential some milivolts but the potential is decreasing like every 2-3 seconds. I thought if temparature and pressure is not changed much it should be fixed... can someone explain the reason of potential change...

 

[Andy Resnick]

In my experience (Ag/AgCl electrodes) the system needs time, up to a few hours, to equilibrate. Try leaving everything in place (with the power off) for an hour and see if the drift goes away.

 

[neuro11]

@Andy, thanks for reply. I will try that...

 

[neuro11]

In my experience (Ag/AgCl electrodes) the system needs time, up to a few hours, to equilibrate. Try leaving everything in place (with the power off) for an hour and see if the drift goes away.

still the drifting exists...can it be the reason that
The concentration of the PBS (does not contain NaCl) solution is 1M whereas the solution inside the salt bridge is 3 M NaCl.

If not, i guess may be the ref electrode is damaged some how...

 

[NascentOxygen]

still the drifting exists...can it be the reason that

I suspect that the problem with your setup is that your meter is continually drawing current from the cell and causing the cell to become polarized. It's only a small cell, you can't draw current without affecting the potential. Maybe if you only momentarily connect the meter to take a quick reading, then leave it disconnected from the cell for, say, 30 mins, before taking another reading might be an acceptable protocol (but I really don't know).

A multimeter with much higher impedance may be better, too.

 

[neuro11]

I suspect that the problem with your setup is that your meter is continually drawing current from the cell and causing the cell to become polarized. It's only a small cell, you can't draw current without affecting the potential. Maybe if you only momentarily connect the meter to take a quick reading, then leave it disconnected from the cell for, say, 30 mins, before taking another reading might be an acceptable protocol (but I really don't know).

A multimeter with much higher impedance may be better, too.

thanks for the advice...
today i took new solution, immerged gold and ref. electrode, left them for hour for equilibrium and then took a 5 min reading. again left for another 20 min or so and took reading...in this way i received better reading...the drift is now 2-3 mv in those 5 mins reading. still acceptable for me.
But what surprising to me is, after that 5 min reading i disconnect the meter. so when i start taking reading again after 20 mins, the starting potential is lower then before. So my question what exactly was using my cell. as i have disonnected the meter the cell potential should not be used up right?