Nickel-ion detection on a boron-doped diamond electrode in acidic media

This work demonstrates the potential to assess Ni(II) concentration in neutral and acidic chloride environments on a boron-doped diamond electrode, without the introduction into the solution of an external chelating agent or markedly raising the pH. The nickel-ion quantification was achieved in solutions with pH values ranging from 8 to 4 using the electrochemical response associated with the Ni(II)/Ni(III) transition on a bare boron-doped diamond electrode. The associated electrochemical reaction was determined to be sensitive to the pH with a dependence relying on a proton stoichiometric number of 0.5 per mole of electrons. The detection protocol consisted of a reagentless electrodeposition of Ni in neutral or acidic solutions followed by oxidation to Ni(II) using differential pulse anodic voltammetry. This allowed the nickel-ion quantification with a limit of detection of 26.1 μM and a linearity over the concentration interval from 10 to 500 μM in a solution pH of 6.2. The regeneration of the pristine electrode surface was also achieved in the sample solution with an electropolishing treatment by holding the applied potential at +1.3 V vs. Ag/AgCl for 30–240 s, thus allowing a fast and efficient surface recovery.