Dropping Mercury Electrode synchronized

The NPV technique was first developed as NP polarography (NPP) at dropping mercury electrodes. In these cases, the pulses are synchronized with the drops, the pulse being applied near the end of drop life when the increase in the surface area of the drop is least. Current sampling in NPP also serves to remove the oscillations resulting from drop formation. 

The greatest advantage of this new type of electrode is its ability to function as a stationary and a nonstationary mercury electrode, as well as the possibility of synchronizing the electrode (drop) formation with the programm-control arrangement. The reproducibility of the mercury metering of an SMDE is important for its dependability in operation. In a commercial model (Multi-Mode electrode, Metrohm AG, Switzerland), the mercury is pushed through the capillary by a ni-... 

The difference between the various pulse voltammetric techniques is the excitation waveform and the current sampling regime. With both normal-pulse and differential-pulse voltammetry, one potential pulse is applied for each drop of mercury when the DME is used. (Both techniques can also be used at solid electrodes.) By controlling the drop time (with a mechanical knocker), the pulse is synchronized with the maximum growth of the mercury drop. At this point, near the end of the drop lifetime, the faradaic current reaches its maximum value, while the contribution of the charging current is minimal (based on the time dependence of the components). 

Figure 4 Modern polarograph, constituted by a potentiostatic system with three electrodes (static mercury, AgCI/Ag reference, and Pt axillary), knocker for synchronism and needle valve allowing to control the size of the hanging drop. With permission of AMEL.

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