Benedict‘s Reagent, also known as Benedict’s Solution, is a light blue chemical reagent named after the American chemist Stanley Benedict. Its preparation principle is as follows: when copper sulfate solution is slowly added to an alkaline solution composed of sodium citrate and anhydrous sodium carbonate, sodium citrate acts as a hydrophilic masking agent, forming a soluble complex salt with copper ions. This effectively prevents the precipitation of copper hydroxide, maintaining the solution in a stable, clear light blue state.
Detection Principle
Under alkaline heating conditions, reducing sugars (including most monosaccharides and disaccharides except sucrose) reduce Cu²⁺ in Benedict‘s Reagent to Cu⁺. The Cu⁺ then combines with OH⁻ to form yellow copper hydroxide (CuOH), which upon heating is rapidly converted to a brick-red cuprous oxide (Cu₂O) precipitate. By observing the color change of the precipitate, the presence and approximate content of reducing sugars in the sample can be determined qualitatively or semi-quantitatively.
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