I'm working with Square Wave Anodic Stripping Voltammetry (SWASV) for detection of heavy metals.
After the deposition step I noticed that the lead's potential peak shifts if I start the stripping step from different potential.
e.g. after 3 mins of deposition at -0.4V (Ag/AgCl), if the stripping step starts from -1V the lead's peak is at -0.2V (Ag/AgCl) while is at -0.4V (Ag/AgCl) if the stipping step starts from -0.6V (Ag/AgCl).
The working electrode is gold and the counter is platinum.
I do the square wave starting from a negative potential to a positive one.
The peak potential should be related to the thermodynamics of the process so I thought is should be 'fixed' fixing the deposition potential and the active material.
Thanks
As Joseph noted, it can be a kinetic parameter. Additionally, if you are starting your scan in the water reduction region, you could be changing the local pH, and hence altering both thermodynamic and kinetic parameters.
Joseph and Leigh: I know that the peak potential could be a kinetic parameter if we speak about under potential deposition (UPD). And of course, fixing the active material (gold in my case) and the analyte (lead), it can change position depending on the kinetics but I didn't think it could change of 200mV due to this. Moreover I can't explain this change of kinetics with the starting potential of SW....
Leigh: I thought about the local pH too. But starting from -1V I produce hydrogen that means increase the local pH. So the peak should go and the left, isn't? In my case, increasing the local pH the peak moves of 200mV in the positive way....
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