Retarding electrode

Slightly downstream of the end of the capillary are usually to be found a filament and/or a discharge electrode, which provided secondary methods of ionization, while opposite or slightly downstream of the sampling cone is a repeller or retarding electrode. Their nse will be described in more detail later. 

Differential potentiometric titration — means the experimental recording of the first derivative of potential over volume of added titrant of a -> potentiometric titration curve. This can be achieved with a -> retarded electrode as developed by - Maclnnes. In a broader sense this term also covers the mathematical derivation of potentiometric titration curves. 

Potentiometric titration — A - titration method based on the measurement of the potential of a suitable -> indicator electrode as a function of - titrant volume. Usually the -> cell voltage or a - p-function associated with the concentration of the - analyte is plotted as a function of the volume of -> titrant added [i]. See also -> differential potentiometric titration, and - retarded electrode. 

Retarded electrode (also called sheltered electrode) —... 

A natural question arises as to whether holding out a portion of the solution while each increment of titrating fluid is added can have an influence on the end point observed. It can be readily shown that the error involved is negligible. Let v be the volume of titrating reagent at the end point, Av the volume of the last increment, and v and V, respectively, the volume of the solution retained around the retarded electrode and the total volume. The error 8 in per cent, will be given by the relation... 

Macinnes invented the use of a retarded electrode for differential potentiometric titrations [vii]. Macinnes also wrote an influential textbook [viii]. 

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