What does a positive biuret test indicate?
Biuret reagent, made of sodium hydroxide and copper (II) sulfate, is used for determining the presence of protein in a sample. The test relies on the reaction between copper ions and peptide bonds in an alkaline solution. A violet color indicates the presence of proteins.
The biuret test (Piotrowski's test) is a chemical test used for detecting the presence of peptide bonds. In the presence of peptides, a copper(II) ion forms violet-colored coordination complexes in an alkaline solution. Several variants on the test have been developed, such as the BCA test and the Modified Lowry test.
- Biuret Reagent is an aqueous solution of potassium sodium tartrate treated with cupric sulfate and sodium hydroxide. In the presence of peptide bonds (protein), this blue solution will change color to pink-purple.
- Since simple sugars (e.g., glucose) give a positive test, the solution is used to test for the presence of glucose in urine, a sign of diabetes. One litre of Benedict's solution contains 173 grammes sodium citrate, 100 grammes sodium carbonate, and 17.3 grammes cupric sulphate pentahydrate.
- In addition to these three elements, plants need a number of minerals for healthy growth. These are absorbed through the roots as mineral ions dissolved in the soil water. Two important mineral ions needed by plants are: nitrate - for making amino acids, which are needed to make proteins.
It is based on the biuret reagent, a blue solution that turns violet upon contact with proteins, or any substance with peptide bonds. The test and reagent do not actually contain biuret; they are so named because both biuret and proteins have the same response to the test.
- The emulsion test is a method to determine the presence of lipids using wet chemistry. The procedure is for the sample to be suspended in ethanol, allowing lipids present to dissolve (lipids are soluble in alcohols). The liquid (alcohol with dissolved fat) is then decanted into water.
- medical Definition of Benedict's solution. : a blue solution that contains sodium carbonate, sodium citrate, and copper sulfate CuSO4 and is used to test for reducing sugars in Benedict's test.
The Biuret Test is done to show the presence of peptide bonds, which are the basis for the formation of proteins. These bonds will make the blue Biuret reagent turn purple. add an equal amount of NaOH to a solution of the food, mix carefully. add a few drops of 1% CuSO4, do not shake the mixture.
- The biuret reaction, in which protein forms a complex with copper (Cu2+) in alkaline solution, has become the standard chemical test for total serum or plasma protein. This complex, which is dependent on the presence of peptide bonds, is blue-purple in color.
- The biuret test uses an alkaline mixture, or reagent, composed of potassium hydroxide and copper sulfate. The normal color of biuret reagent is blue. The reagent turns violet in the presence of peptide bonds -- the chemical bonds that hold amino acids together.
- Add the food sample to 2 cm3 of ethanol, shake well. Allow to settle in a test tube rack for 2 minutes for food to dissolve in ethanol. Empty any clear liquid into a test tube containing 2 cm3 of distilled H2O. A MILKY-WHITE EMULSION is a positive result: lipid is present.
Updated: 2nd October 2019