I am trying to detect Calcium in PBS. I am use an Ag/AgCl reference electrode, glassy carbon working electrode and platinum wire counter electrode. I am using PBS pH 8.5 with 0.5 MgCl2 as the electrolyte solution.
I did a background scan of PBS, then added 1mM CaCl2 to the PBS. I was able to see a clear reduction peak (see attached picture) at -0.110V. Since The PBS + MgCl2 already contains Chlorine, I assumed that this peak was due to the calcium.
Then I tried to see the difference between different additions of CaCl2 to PBS (333uM, 666uM and 1mM) using CV. Sometimes I saw a reduction peak at the expected potential (-0.110V) and other times I did not - independedent of the addition of CaCl2 to the solution. For instance, in one experiment, I did a CV with 1mM CaCl2 added, and did not see the peak, I cleaned the electrode, repeated the measurement, and afterwards I did see it.
I have cleaned the electrode with alumina between each measurement, made sure there are no bubbles attached to either the working or counter electrode.
Can anyone suggest how I can troubleshoot this experiment so that I can get reproducible measurements?
Nico Crudele record voltammograms out of PBS, and you maybe will know if your problem is related with the PBS medium.
Beside the good opinion of Javier Ernesto Vilaso Cadre . You need to narrow range of CV to -1 to +1 V. because you has an observed O2 Evolution peak. and repeat process at 4 scan rates (100, 50, 20, and 10) mV/s
Nico Crudele, the reduction potential for calcium beyond -2.7 V, and compared with your blanke, the evaluation of oxygen is decreased, and one peak may belong to the electrolyte's deposition from the first scan.
There is a close relationship between the variation of the potential and the change of the morphology of the surface, the fact of scanning the potential causes the change of the morphology and subsequently the displacement of the potential.
thank you all for the answers! I ended up changing the experiment, where I was no longer interested in Calcium detection. One thing I noticed was that the reduction peak at -0.110V only occurred after a forward scan to the high potential. This leads me to believe that it is due to some change from reaching the oxygen evolution peak.
This is normal when scanning the potential between two surface morphology values.
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