Fig. 3 explains the reduction and oxidation steps proceeding at the
electrode surface in a schematic way. Fig. 4 shows differential pulse
scans following a preliminary reduction of the AgCl crystals at −0.7 V
(vs. SCE) for 60 s, and the corresponding calibration plot. The sensitivity
of the silver determination is 0.094 A L mol−1 and the detection limit
was calculated as 2.3 × 10−6 mol L−1 (1.16 × 10−11 mol). Considering
the surface treatment of the electrode, with SiC grinding papers up to
4000 grit, is highly likely to decrease the detection limit if the surface
roughness is reduced, for example,mechanically polishingwith alumina
powder up to 0.05 μm. That is, assuming that the process of reducing the
surface roughness does not affect the adhesion of the crystals formed by
precipitation. The here described precipitation–immobilization protocol
is potentially applicable also as a calibration-free method, provided
the determination is performed as coulometry (chronocoulometry). In
the case of AgCl this was not possible because of the layer by layer
conversion of theAgCl crystals. For compoundswhich can be completely
transformed in a stoichiometric electrochemical reaction (for examples
see [19]) calibration-free determinations based on coulometry will
certainly be possible.