Which total protein method requires copper sulfate, potassium iodide in sodium hydroxide, and potassium sodium tartrate in its reagent system?

Which total protein method requires copper sulfate, potassium iodide in sodium hydroxide, and potassium sodium tartrate in its reagent system?

• A. Kjeldahl
• B. Biuret
• C. Folin-Ciocalteu
• D. Ultraviolet absorption

Answer: (B)

The Biuret reaction for total protein detection relies on copper ions forming a complex with peptide bonds in an alkaline medium. Copper sulfate supplies Cu2+; sodium hydroxide creates the strong base environment that enables peptide nitrogens to coordinate with the copper ion, producing a color change. Potassium sodium tartrate acts as a stabilizing agent, keeping the copper-peptide complex in solution and enhancing the color yield, which makes the assay more sensitive and reliable. The violet color produced correlates with the amount of peptide bonds, and thus with total protein. Other common total protein methods don’t use this copper-based, tartrate-stabilized system—the Kjeldahl method digests protein to measure nitrogen, the Folin-Ciocalteu approach targets reducing capacity rather than peptide bonds, and ultraviolet absorption measures protein directly without this specific reagent chemistry.

The Biuret reaction for total protein detection relies on copper ions forming a complex with peptide bonds in an alkaline medium. Copper sulfate supplies Cu2+; sodium hydroxide creates the strong base environment that enables peptide nitrogens to coordinate with the copper ion, producing a color change. Potassium sodium tartrate acts as a stabilizing agent, keeping the copper-peptide complex in solution and enhancing the color yield, which makes the assay more sensitive and reliable. The violet color produced correlates with the amount of peptide bonds, and thus with total protein. Other common total protein methods don’t use this copper-based, tartrate-stabilized system—the Kjeldahl method digests protein to measure nitrogen, the Folin-Ciocalteu approach targets reducing capacity rather than peptide bonds, and ultraviolet absorption measures protein directly without this specific reagent chemistry.