Channel electrodes numerical methods

The mass transfer by convection and diffusion within the channel is precisely calculable. Numerical methods are used to fit measured concentrations at the detector electrode to the fluid flow in the cell, and to the reaction kinetics at the surface and in solution [24]. The technique was extensively developed during a study of the dissolution of calcite in dilute aqueous acid [25], and has latterly been applied to a number of organic reactions. 

In these techniques, the excited atom source is not a flame but a plasma e.g. Ar plasma, a d.c. or a.c. arc or a spark. Since higher temperatures are achieved in plasmas, excited ions may be also formed as well as excited atoms. In any case, the lines are more numerous than in other techniques. The lines to be detected are selected by narrow band pass monochromator and are detected by sensitive photomultipliers. The functions of the instrument are controlled by a micro-processor and are displayed on a photographic plate, a cathode ray tube, a recorder or a printer. Qualitatively, the lines obtained from a sample are compared with tables compiled for various elements as atoms or ions. The latter are more intense when plasmas are used. The presence of 3 major lines of an element is taken as positive identification. Most elements can be identified by these methods. Solid samples can be embedded in an electrode of the source. Quantitative analysis is possible for instruments giving an intensity reading. By assigning a channel for each element, the measured intensity depends on the amount of element present. 

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