Voltammetry

Voltammetry is a collective term for various electroanalytical methods for qualitative and quantitative analysis of a sample with which one can determine the chemical composition of mixtures on the basis of the voltage-dependent current profile, as well as for the elucidation of reaction mechanisms.

The word is a portmanteau of voltammetry and amperometry volts and shows that the basis of voltammetry current-voltage curves. In the measurement of the current intensity between the two solid-state electrodes, the voltage is varied with time. (In contrast, in the voltammetry ( the voltage U is measured with a "m "). )

This procedure is a form of electrolysis in liquids or gases, in which it is found that specific chemical constituents are accelerated by the forming fabric distribution particularly at a typical voltage them. The passage of the reaction leads to a sudden increase in current, when the electric field is sufficient to oxidize the molecules, atoms or ions in the double layer, or to be reduced. Features of this reaction is a passage of electrons through the interface between the electron conductor and the electrolyte.

The analysis of current-voltage curves represents an in electroplating, especially in alkaline zinc plating and acid copper plating, the preferred method for evaluating the deposition conditions dar. Here not only - evaluated individual sections, but the entire curve as a sum parameter - as outlined above.

Stripping voltammetry / stripping voltammetry

In this form of a voltammetry enrichment step is carried out before the potential scan. The goal is to get through the capture of the analyte at the working electrode larger voltammetric signals to allow quantitative measurements in the ultra trace range. There are different possibilities. Through electrolysis metal ions can be reduced to the metal and deposited as a very thin layer at the working electrode. In the case of mercury as an electrode material ( hanging drop or film) while an alloy is formed mostly. The metal dissolves in liquid mercury. In particular, metal complexes and organic analytes can be deposited by adsorption on the working electrode. The enrichment of the analyte causes a lowering of the limit to the factor of 1000.

Example: Cadmium ions are deposited at a mercury electrode in the enrichment step:

In a reversal, the so-called stripping, the deposited cadmium is oxidized anodically again:

Here, the current-voltage curve is recorded, with the case of linearly varying voltage peak currents occur which are registered. About the recorded chart statements can be made about the original concentration of the metal ion in the solution to make if you have previously created calibration curves. It is in the reverse process, other methods of determination, eg applying coulometry, wherein the mass of the previously deposited material can be calculated in this case the determined load.

If two or more metal ions present in the solution so formed during the anodic redissolution several current peaks which can be assigned to different metal ions according to previously generated calibration curves.

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