Which assay method is commonly used for drugs containing calcium and zinc?

Which assay method is commonly used for drugs containing calcium and zinc?

• A. Gravimetry
• B. Precipitimetry
• C. Acidimetry
• D. Complexometry

Answer: (D)

Complexometry uses a chelating agent, typically EDTA, to form stable complexes with metal ions in a sample. In pharmaceutical analysis, drugs containing calcium and zinc are commonly treated with EDTA in a buffered solution, and the amount of metal present is determined by titrating until all metal ions are bound by EDTA. The endpoint is detected with a suitable indicator that changes color when free EDTA remains, signaling that the metal ions have been fully complexed.

This approach is especially well-suited for calcium and zinc because these divalent ions form highly stable, protein-friendly complexes with EDTA over the range of conditions used in drug analysis. It provides precise, selective measurements even in the presence of other ions and complex matrices, making it the method of choice for determining metal contents in such drugs. Gravimetry and precipitation-based titrations rely on mass changes or insoluble products and are less convenient for routine analysis of calcium or zinc in formulations, while acidimetric methods are about acid content and do not target metal ions.