Chelatometrie

Chelatometry is a quantitative analytical technique used to determine the concentration of metal ions in solution. It is based on the principle of chelation, where a metal ion forms a stable complex with a ligand, such as an organic acid or its derivative. The most commonly used ligand in chelatometry is ethylenediaminetetraacetic acid (EDTA).

In a typical chelatometric titration, a known volume of a standard solution of the metal ion is titrated with a solution of the ligand. The endpoint of the titration is detected by a change in the electrical conductivity of the solution. This change occurs because the formation of the metal-ligand complex reduces the number of ions in solution, thereby decreasing the solution's conductivity.

The endpoint of the titration can also be detected using a pH meter or a colorimetric indicator. The pH of the solution changes as the metal ion is complexed by the ligand, and this change can be used to determine the endpoint. Colorimetric indicators change color in the presence of the metal-ligand complex, providing a visual indication of the endpoint.

Chelatometry is a versatile technique that can be used to determine the concentration of a wide range of metal ions, including calcium, magnesium, iron, and copper. It is particularly useful in the analysis of complex matrices, such as biological samples, where other analytical techniques may not be suitable.

One of the advantages of chelatometry is its high sensitivity and selectivity. The technique can detect very low concentrations of metal ions, and the use of specific ligands allows for the selective determination of a particular metal ion in the presence of others.

However, chelatometry also has some limitations. The technique requires the use of specific ligands for each metal ion of interest, and the formation of the metal-ligand complex must be stable and reversible. Additionally, the technique may not be suitable for the analysis of very dilute solutions or for the determination of metal ions in the presence of strong complexing agents.

In summary, chelatometry is a valuable analytical technique for the determination of metal ion concentrations in solution. It is based on the principle of chelation and can be used to detect the endpoint of a titration using electrical conductivity, pH, or colorimetric indicators. While it has some limitations, chelatometry is a versatile and sensitive technique for the analysis of metal ions in complex matrices.