Flow electrochemical analyses of zinc by stripping voltammetry on graphite felt electrode.

A flow sensor for trace analysis of zinc, using graphite felt as working electrode is reported here. A flow cell, well-adapted to 3-D porous electrodes and capable to do both the preconcentration step at a cathodic potential and the stripping of the zinc was successfully developed. It was demonstrated that this cell allows to obtain better electrochemical signals for Zn(2+) compared to a standard three-electrodes cell and that the percolation during accumulation increases the kinetics of electrodeposition. The influence on Zn(2+) signal of the deposition potential, the time of deposition and the flow rate was studied. The resulting sensor shows a linear response towards Zn(2+) with a linear range of 10(-6)-10(-4)M and a limit of detection of 5×10(-7) M for an analysis time of 5 min. The interferences study showed that the Cr(3+), Pb(2+), Cd(2+) ions have a small effect on the Zn electrochemical signal, whereas Fe(3+), Cu(2+), Co(2+) and Ni(2+) ions strongly influence it. The electrode was tested on real samples (tap water spiked with Zn(2+), food supplement) with a good recovery by applying the standard addition method.