Why is it necessary to identify the reducing sugar Filin reagent to solution A and solution B, and t

First of all, we must understand the principle of Filin reagent;

Feilin reagent is a suspension of light blue Cu(OH)2 precipitated prepared by a certain concentration of sodium hydroxide and copper sulfate, and the glucose solution is reduced to a brick-red precipitate under heating conditions after adding Feilin reagent, and glucose is oxidized to gluconic acid. Its reaction formula is:

ch2oh—(chohh)4—cho + 2cu(oh)2 → ch2oh—(choh)4—cooh + cu2o + 2h2o

Sodium hydroxide solution and copper sulfate solution are liquid A and liquid B, which are mixed and reacted to Cu(OH)2, so both must be used.

Filin reagent and biuret reagent.

Both the Filin reagent and the biuret reagent are composed of NaOH solution (there is also potassium sodium tartrate in the Filin reagent) and CuSO4 solution, but there are three differences between the two:

1) The concentration of the solution is different.

The CuSO4 solution is called Filin reagent B and its concentration is g ml;

The concentration of CuSO4 solution (biuret reagent B) is in g ml.

2) The principle of use is different.

Fillin's reagent is a newly formulated solution that reacts with an aldehyde group under heating conditions and is reduced to a brick-red precipitate that can be used to identify the presence of soluble reducing sugars. When the soluble reducing sugar is identified with Filin reagent, the color change process of the solution is: light blue, brown, brick red (precipitate).

When identifying whether a protein is present in a biological tissue, the biuret method is commonly used, using a biuret reagent, and a biuret reaction occurs. Compounds with two or more peptide bonds can react purple with biuret reagents. The peptide bond of the protein can be complexed with Cu2+ in alkaline solution to form purplish-red compounds.

The shade of color is directly proportional to the protein concentration.

3) Different ways to use it.

When Feilin reagent is used, first mix the two liquids A and B in equal volume, and then use it immediately, and the reaction needs to be heated (sometimes it is also reacted without heating); When using the biuret reagent, first add NaOH solution (2ml), shake well to create an alkaline reaction environment, and then add 3 4 drops of CuSO4 solution, shake well and observe the phenomenon.

The concentration of NaOH solution (solution A) in Filin reagent is , the concentration of CuSO4 solution (solution B) is , and the concentration of solution A in the diuret reagent used to identify proteins is the concentration of solution B, and the concentration is not the same, so it cannot be used directly.

It's easy to understand if you explain it from the principle:

The Felin reagent for the identification of soluble reducing sugar is the Cu(OH)2 solution prepared with solution A and solution B that reacts with the aldehyde group under heating conditions, and is reduced to a brick-red precipitate. The dosage ratio of solution A and B is 2:

1 to generate Cu(OH)2.

To determine whether a solution contains protein, a biuret reaction is used. The diuret reaction is essentially a purple reaction between Cu2+ and protein in an alkaline environment. Therefore, the concentration of solution B (CuSO4) should not be too large, otherwise too much blue Cu2+ will interfere with judging whether the solution is purple.

Films identify sugar. The essence of protein is an enzyme, so naturally it cannot be directly identified by film, and you confuse the chemical properties and identification principles of protein and sugar.

The concentration of copper sulfate in the Filin reagent and the biuret reagent is different.

First of all, you have to know what the three reagents do. The biuret reagent is to test protein, the Filin reagent is to test glucose, and as for the starch solution, under the action of amylase, it can be hydrolyzed into glucose.

1) The above four solutions are divided into 2 groups with a reagent, which is a diurea reagent, in which the group of chromogenic reactions is dilute egg white and amylase solution, and the glucose and starch solutions that do not undergo chromogenic reactions.

The key here is that you should know that the main component of enzymes is proteins.

2) Use Filin reagent to distinguish a group of solutions that do not undergo chromogenic reactions.

3) Distinguish the method and results of a group of solutions in the chromogenic reaction: take a little of each of the two solutions in the chromogenic group, put them in different test tubes, add 5 drops of starch solution dropwise, shake fully, and stand for half an hour. The Feilin reagent is added to the reaction solution after standing, and the brick-red precipitate is the amylase solution.

(1) Because the essence of dilute egg white and amylase solution is protein, protein can react purple with biuret reagent, while glucose and starch belong to sugars and cannot react with biuret reagent, so the four solutions can be divided into two groups with biuret reagent

2) Glucose is a reducing sugar, which can be identified with Feilin reagent, while starch cannot, and can be distinguished between glucose solution and starch solution by Feilin reagent

3) Amylase can decompose starch into maltose, maltose is a reducing sugar, so after adding starch, it is amylase that appears after the brick-red precipitate is identified by Feilin reagent Therefore, the starch solution can be mixed with the two solutions that have a color reaction, and after a period of time, the above two mixtures are treated with Feilin reagent respectively, and the egg white solution is diluted when the solution without color change is observed, and the amylase solution is brick-red

Therefore, the answer is: 1) biuret reagent, thin egg white, amylase, glucose, starch.

2) Filin reagent.

3) Mix the starch solution with the two solutions that have a chromogenic reaction, and after a period of time, treat the above two mixtures with Feilin reagent respectively, and observe that the solution without color change is dilute the egg white solution, and the brick red color is the amylase solution.

Summary. If the sample contains monosaccharides (such as glucose, fructose, etc.), it will produce green fluorescence under the action of the Filin reagent. If the sample contains disaccharides (such as sucrose, galactose, etc.), it will produce yellow fluorescence under the action of the Filin reagent.

When using Filin reagent to identify apple tissue sample fluid, can monosaccharides and disaccharides be distinguished?

If the sample contains monosaccharides (such as glucose, fructose, etc.), it will produce green fluorescence under the action of the Filin reagent. If the sample solution contains disaccharides (such as sucrose, galactose, etc.), it will produce yellow fluorescence under the action of Filin reagent.

Therefore, monosaccharides and disaccharides can be identified when using Filin reagent to identify apple tissue-like fluids.

Extended information: Filin reagent is a chemical reagent commonly used to identify monosaccharides and disaccharides. It is composed of a mixture of suna alkali (R-Su) and isoacrolein (IAA).

When detecting reducing sugars with Filin reagent, liquid A and solution B should be mixed evenly and then added, and water bath heating is required

Therefore, c

Same. We designed three sets of experiments (I explained the principles of experimental design to my students when designing the experiments):

1.Take three test tubes A, B, and C, and add 2ml of apple tissue sample solution respectively.

2.Add 2ml of freshly prepared Feilin reagent (2ml of solution A and 4 drops of solution B mixed evenly) to the test tube A, shake well;

Add 2ml of Filin reagent solution A to the B test tube, mix evenly, and then drop 4 drops of solution B, shake well;

Add 4 drops of solution B to the C test tube, mix well, and then add 2ml of Filin reagent solution A, shake well.

3.Heat the three tubes together in 100 °C boiling water and observe the color change in the three tubes.

Experimental results: The color change order of the three test tubes was from blue brown to brick red, and the degree and speed of the color change of the three test tubes were basically the same, with obvious discoloration after about 17 seconds, and significant red bricks after one and a half minutes. We repeated the above experiment three more times, and the experimental phenomenon was the same as the first time.

In the whole experimental process, we only have the order of Gafilin reagent A and B, and the others are exactly the same, strictly following the principle of single factor variables in control experiments.

We analysed the experiments based on the data we found:

The first possible reason: liquid A and then liquid B cannot be added first, because this operation is more alkaline. The students immediately calculated the NaOH concentrations for both operations:

Add 4 drops dropwise to the Filin reagent solution (approximately, the NAOH in the solution is only reduced. The alkalinity of the mixture of A and B is slightly lower than that of the first solution, but the difference is very small. Therefore, compared with the procedure required in the book, the alkalinity of the tissue-like solution changes very little.

Therefore, if the alkaline solution is to avoid changing the structure of the reducing sugar, then the operation in the book will also change the structure of the reducing sugar.

The second reason: the reason why solution B and then solution A cannot be added first is because CuSO4 has to react with reducing sugar. But after consulting several books, there is no such elaboration. Later, I asked a few chemistry teachers, and they also said that the reaction would only occur under alkaline and heating conditions.

Since it does not react, it creates an alkaline environmental condition regardless of the order in which it is added. According to data 3, Cu2+ or Cu(OH)2 reactions generate brick-red precipitates. Therefore, regardless of the order in which they are added, reducing sugars can be identified. See.