Biuret protein testAnhydrous copper sulfate has strong water absorption. When it is put into 95% ethanol or water-containing organic matter, it absorbs water and returns to blue crystals. The copper ions in copper sulfate can destroy the three-dimensional structure of protein and denature it. When measuring protein concentration, alkali is often added to the protein, and then copper sulfate solution is added. At this time, the solution will turn purple. This reaction is called the biuret reaction.

The method of biuret protein test does involve anhydrous copper sulfate, and anhydrous copper sulfate does have strong water absorption. The following is a detailed explanation of these two points:

Biuret protein test

The biuret method is an analytical method for identifying proteins. Biuret is the product obtained by heating two molecules of urea to release one molecule of ammonia. In a strong alkaline solution, biuret forms a purple complex with divalent copper ions. This reaction is called the biuret reaction. Since protein molecules contain peptide bonds similar to the biuret structure, similar color reactions can also occur. The color depth of the purple complex is proportional to the protein concentration, but has nothing to do with the protein molecular weight and amino acid composition, so it can be used to determine the protein content.

Biuret reagent is an alkaline copper-containing test solution that is blue and is used in the biuret reaction. It is prepared from 1% potassium hydroxide, a few drops of 1% copper sulfate (here copper sulfate is the real active ingredient in the biuret reagent) and potassium sodium tartrate. Among them, the mass fraction of copper sulfate solution is usually 0.01g/mL. Potassium hydroxide is only used to provide an alkaline environment (so it can be replaced by other bases such as sodium hydroxide). Adding potassium iodide to the reagent can extend the service life of the reagent.

Water absorption of anhydrous copper sulfate

Anhydrous copper sulfate (chemical formula: CuSO4) is a white or off-white powder, the solution is acidic, and the dust is very pungent. Its density is 3.603 g/cm3, and its solubility in water at 25°C is 23.05 g/100 g water. It is insoluble in ethanol and ether. Anhydrous copper sulfate has strong water absorption. When it comes into contact with water, it changes from white to blue, generating copper sulfate pentahydrate (CuSO4·5H2O). Therefore, it can be used to test the existence or generation of water in chemical reactions and absorb water vapor.

In general, in the process of biuret protein testing, anhydrous copper sulfate, as part of the biuret reagent, plays a role in reacting with the peptide bonds in the protein to form a purple complex. At the same time, its strong water absorption has also been widely used in other chemical fields.