Metal complexes-dyes are used in many branches of analytical chemistry. For example, most of dyes form complexes with pollutants in aqueous media. They are used as titrations indicator in analytical chemistry, and their complexes with the metal ions in aqueous media are used in spectrophotometric analysis. In general, the complexation between dyes and some essential metals allows the detection of them by the photometric analysis and electrochemical analysis.
Application in practice
The formation of complexes amplifies the differences in properties between metal ions, e.g., colour, solubility and stability all vary considerably depending on how the complexes are formed, which creates good conditions for the analysis and separation of metal ions. Dye complexes have potential applications in the following two main areas of analysis.
- Applications in photometric analysis
Most of dyes (e.g., azo dyes) form complexes with the metal ions (e.g., Cu (II), Hg (II)) in aqueous media are used in photometric analysis. These dyes interact easily with metal ions through the heteroatoms S, N, and O and can chelate with a large number of metal ions to form a metal-dye complex. By UV-Vis spectrophotometry, the absorption spectra of solutions allow the determination of metals concentration. The principle of the analytical assay is described below. The absorption spectra of dye solution and metal ions solutions are measured first. Then, after the mix of the dye and the metal ion, the formation of coloured complex between the both compounds give a new color peaking and a new absorption spectrum. This significant change is an indirect indication of the concentration of the metal ion.
- Applications in electrochemical analysis
In electrochemistry, the metals complexation with dyes has been investigated for the selective determination of metals trace by voltammetric techniques. For this, the oxidation/reduction current of dye is measured in the presence and the absence of metal ions. The decrease of the redox peaks caused by the formation of electro inactive complexes is function of the metals concentration.
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