DC Polarography with the DME and SMDE Modes

The condenser current can not be eliminated and, in point of fact, it is the factor that restricts the limit of detection of the DME in the straight-forward dc mode and tast dc mode to about 10 M. The minimization of this factor can be accomplished by the use, for example, of the differential pulse mode, and this will be discussed later. 

The faradaic component of residual current due to impurities can be minimized by the thorough removal of dissolved oxygen by flushing the solution with an inert gas such as nitrogen or argon by the use of double-distiUed water or distilled deionized water, and by the use of high-purity chemicals. 

The Ilkovic equation [31] relating diffusion current and analyte concentration has a component which refers to the fact that the surface area of each mercury drop grows before it falls off the capillary due to the effect of gravity. Under these conditions the time to fall-off is called the drop hfe. Selected drop times are obtained by tapping the capillary to induce earher drop fall-off. This component is  

The effect of the drop surface moving into the solution is compensated for hy multiphcation of the rate of diffusion by the factor (7/3) 2. A combination of these factors leads to the equation for an electrode reaction  

Substitution of the value for the faraday and the density of mercury at 25 C yields the expression  

---