Murexide

Murexide, also known as ammonium purpurate, is a chemical compound used as an indicator in complexometric titrations, particularly for determining the concentration of calcium ions. It is an ammonium salt of purpuric acid.

Chemical Properties: Murexide is a purple solid. In aqueous solution, its color varies depending on the pH. At highly acidic pH, it is yellow. As the pH increases, the solution transitions through reddish-purple, and becomes blue-violet at alkaline pH. These distinct color changes make it useful as a visual indicator.

Applications:

• Complexometric Titration: Murexide is primarily employed as an indicator in complexometric titrations with EDTA (ethylenediaminetetraacetic acid). It forms complexes with various metal ions, including calcium, nickel, copper, and cobalt. The color change at the endpoint signals the completion of the titration. It is especially suitable for titrations where a sharp endpoint is desired and other indicators may be less effective.
• Analytical Chemistry: Beyond titrations, murexide has found applications in analytical chemistry for the spectrophotometric determination of certain metal ions.
• Historical Significance: Murexide was one of the earlier complexometric indicators. Its use predates the widespread adoption of other, more modern indicators.

Synthesis: Murexide is typically prepared by heating guanine with nitric acid, followed by neutralization with ammonia.

Safety: Murexide is generally considered to have low toxicity. However, as with any chemical, it should be handled with appropriate precautions, including wearing gloves and eye protection. Information on specific hazards can be found in the material safety data sheet (MSDS).