Quantitative benedict test using bicinchoninic acid

Cupric ion (Cu2+), in complex form, functions as a selective oxidizing agent for a variety of compounds in the qualitative Benedict test. Cupric ion is reduced to cuprous ion (Cu+) in the reaction. We found that the cuprous ion formed in this type of redox reaction could be detected and quantified using 2,2'-bicinchoninic acid. This reagent produced an intense purple complex with cuprous ion. The color development in this modified Benedict test was dependent on pH, temperature, and time. The reaction is insensitive to ethanol and sodium dodecyl sulfate. This improved method of the Benedict test has enhanced sensitivity and makes the quantitation of compounds possible. This method should be useful for studies of Benedict-positive compounds which are available only in small amounts.