Biuret reagent contains which components?

• A. Potassium hydroxide and copper sulfate
• B. Sodium hydroxide and copper nitrate
• C. Ammonia and copper chloride
• D. Calcium hydroxide and copper acetate

Answer: (A)

Biuret reagent works because it needs copper(II) ions in a strongly alkaline solution to form a purple complex with peptide bonds. The reagent uses copper sulfate as the source of Cu2+ ions and potassium hydroxide to create a high pH environment. In this alkaline medium, peptide bonds can coordinate with the copper ions, producing the characteristic purple color that indicates the presence of proteins or peptides. The other options don’t provide the exact combination of copper(II) ions with a strong base in the right form, so they wouldn’t yield the same color change.