SENSORS AND SAMPLE PREPARATION IN STRIPPING VOLTAMMETRY

The great choice of electrode reactions, electrode materials, electrode designs and registration modes is the basis for various sensors for stripping voltammetry (SV) development. The most important are mercury drop and carbon electrodes. The use of epoxy-impregnated graphite disk electrodes and thick-film graphite disposable electrodes in SV in comparison with glassy carbon electrodes was studied. Surface regeneration, the possibility of using electrodes as sensors in adsorptive stripping voltammetry (AdSV) and organic compounds (natural or pollutants) that affect the responses of elements were investigated. Two kinds of electrode reactions which are in use in SV were considered: discharge ionization of metals that are the basis of ASV and metal complex or special reagent sorption that are the basis of AdSV and modified electrodes. In the first case, a mercury preplated or in situ plated electrode is usually used. Low reproducibility in comparison with mercury electrodes is characteristic of such electrodes owing to non-uniformity and delay in mercury deposition on the electrode surface. It was shown that such difficulties can be eliminated by mercury deposition in the presence of metal ions with a small electronic work function, which are capable of forming adatoms on the electrode surface. Determination of Cr and W ions is considered as an example of the application of carbon electrodes in AdSV. Advantages of graphite electrodes over glassy carbon electrodes are better adsorbability of organic compounds, aromatics in particular, which makes it possible to use the electrodes in AdSV. Electrochemical sample preparation consists of two stages: organic compound oxidation and reduction of excess of oxidant without loss of the metals to be determined. Investigation of model solutions containing natural and artificial surfactants and complex-forming compounds and natural and waste waters showed the possibility of the use of graphite electrodes as sensors in the SV of the above-mentioned materials. The examples considered confirm the following advantages of thick film disposable electrodes: they are less sensitive to organic substance content than disc impregnated electrodes; and their properties are similar to those of microelectrode arrays.