Reaction principle: Under heating conditions, Feyning reagent and soluble reducing sugar (glucose, fructose, maltose) can generate brick red cuprous oxide precipitate. Therefore, Fehling reagent is often used to identify the existence of soluble reducing sugar.
Ferrin reagent is a potassium sodium tartrate complex of copper ion, which can be reduced to cuprous oxide by aliphatic aldehyde or reducing sugar. Linfei reagent is a dark blue solution. When heated with aliphatic aldehyde or reducing sugar, the blue color disappears and red cuprous oxide precipitates.
In the process of cuprous oxide precipitation, the color of the reaction solution may gradually change from blue to green, then to yellow, and then to red precipitation. When the reaction is fast, red precipitation is directly observed.
Extended data
The preparation and use methods of Linfei reagent are as follows:
Preparation method: 0. 1 g/ml sodium hydroxide (solution a) and 0.05g/ml copper sulfate (solution b). Solution A was prepared by dissolving 50g sodium hydroxide and 137g potassium sodium tartrate in 500m distilled water (stored in a bottle with a rubber stopper). Solution B was prepared by dissolving 34.5 g of crystalline copper sulfate in 500 ml of water and adding 0.5ml of sulfuric acid. Mix evenly.
Usage of Phyllin reagent: Generally, mix solution A and solution B of Phyllin reagent in the same volume (or drop 4-5 drops of solution B into 2 mL of solution A), then pour the mixed Phyllin reagent into the solution to be tested, and heat it in water bath or directly (Biology Compulsory for Senior High School Education Edition 1 60℃ water bath heating). If there is reducing sugar in the solution to be tested, brick-red precipitation will appear; If there is no reducing sugar in the solution to be tested, it is still blue.
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