chelometric

Chelometric is an adjective relating to chelometry, the branch of analytical chemistry that quantifies metal ions by forming stable complexes with multidentate ligands (chelators). The term emphasizes the role of chelation in measurement and is applied to techniques, procedures, and data that rely on complex formation to determine metal content. The word derives from chelate, from the Greek chēlē “claw,” and the -metric suffix indicating measurement.

Principles: In chelometric methods, metal ions in solution react with a chelating agent to form a defined complex with known stoichiometry and stability constants. Stability, ionic strength, and pH influence the reaction and must be controlled. The most common chelator is ethylenediaminetetraacetic acid (EDTA), which forms stable complexes with many divalent and trivalent metals. In complexometric titrations, the metal concentration is inferred from the amount of chelator needed to reach an end point, often indicated by metallochromic indicator dyes such as Eriochrome Black T, murexide, or similar indicators. Spectroscopic or potentiometric detection can also be used.

Applications: Complexometric titration is widely used to determine water hardness (calcium and magnesium), quantify trace metals in environmental samples, analyze pharmaceuticals, and measure metal ions in biological fluids. It is valued for selectivity when proper buffering and masking agents are employed.

Limitations and considerations: Interference from competing ions, pH sensitivity, and the need for suitable masking agents can complicate measurements. Calibration and careful control of ionic strength are essential for reliable results.