Electrochemical Stripping Analysis
In analytical chemistry the analyst is often faced with the measurement of trace materials that frequently imposes the need for some method of concentration. The common method used for analyte concentration is some form of chromatography but electrochemical stripping is sometimes an alternative and under some circumstances can be a more suitable and efficient concentrating procedure. In this procedure the concentration and subsequent stripping can be accomplished at the same working electrode. As a consequence the stripping technique can be an effective, rapid, sensitive and simple method of trace analysis. The system also significantly reduces the probability of contamination, as very little use of reagents is necessary, if any at all.
As the stripping technique allows concentration factors of more that two to three orders of magnitude to be realized, the technique can be used to determine substances present at levels down to 10-11 M and can measure four to six different analytes in one determination. The technique has been used very successfully in the fields of environmental, clinical, food and pharmaceutical chemistry. It is also a common technique us to determine element speciation in water samples. It has been established that the procedure has been successfully employed in the measurement of forty different elements at trace concentration levels and many organic compounds of biochemical interest.
Stripping analysis consists of two basic (and sometimes a third) procedure(s). Firstly, the adsorption or desorption of the analyte(s) onto the working electrode is carried out over a given time period. Secondly (an elective procedure) the sample matrix may be changed to improve the stability of the measurement and/or the sensitivity of the analysis. Finally the concentrated material is oxidized or reduced back into solution from the working electrode. This can be carried out by programming the working electrode potential over a given time period, applying a fixed electrode current or by chemical oxidation.
At this time it would be appropriate to define the three different procedures that are employed. Stripping Voltammetry (SV) involves the analysis of an accumulated analyte by monitoring the current while programming the applied potential.
Stripping chronopotentiometry (SCP) is the determination of an accumulated analyte by monitoring the change in electrode potential with time while stripping at a constant rate. The time between two significant changes in electrode potential will be a function of the analyte concentration.
Stripping tesammetry (ST) is the determination of an accumulated analyte by measuring the capacitance current produced by a desorption process occurring during a potential scan. Two of these procedures will be discussed, Stripping Voltammetry (SV) (Anodic) and Stripping chronopotentiometry (SCP).