Estimation of Carbohydrates by the Anthrone Method

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Carbohydrates are a significant component of storage and structural materials in plants. Carbohydrates are stored as free sugars and polysaccharides, and the basic units of carbohydrates are Monosaccharides.

When hydrolyzing the carbohydrates, they give monosaccharides, but they cannot be split into simpler sugars when hydrolyzing monosaccharides. The resultant monosaccharides estimate the hydrolyzed product of polysaccharides.

Principle

Carbohydrates are dehydrated with concentrated H2SO4 to form “furfural,” which condenses with Anthrone to form a green color complex that can be measured colorimetrically at 620nm (or) by using a red filter. Anthrone reacts with dextrins, monosaccharides, disaccharides, polysaccharides, starch, gums, and glycosides. But the yields of color are from carbohydrates to carbohydrates.

The Anthrone reagent detects carbohydrates (polysaccharides and oligosaccharides) in proteins and lipids. Saccharide units present in protein, glycopeptide, or glycolipid serve as reactants under the condition. Aqueous acidified anthrone reagent hydrolyses saccharides into monosaccharides and catalyzes the condensation of a hydroxyl group (OH) with naphthol liberated by hydrolysis to form a naphthononolactone derivative. After washing, the colorless fluorescence is intensified by decolorization with sulphuric acid followed by the Anthrone test substrate.

Carbohydrates are dehydrated by conc.H2SO4 to form furfural. The active form of the reagent is anthranol, the enol tautomer of Anthrone, which reacts by condensing with the carbohydrate furfural derivative to give a green color in dilute and a blue color in concentrated solutions, which is determined colorimetrically. The blue-green solution shows an absorption maximum of 620 nm. 

(i) Hydrolysis to monosaccharides 

Disaccharide → Monosaccharide 

(ii) Dehydration—product is a furfural 

Monosaccharide → Furfural 

(iii) Reaction of furfural with Anthrone 

Furfural + Anthrone reagent → Blue-green complex.

Reagents

  1. Anthrone reagent:  Dissolve 200mg of anthrone reagent in 100ml of concentrated H2SO4.
  2. Standard Glucose solution: a) Stock standard: Weigh 100mg of glucose and transfer it carefully into 100ml of distilled water. (100 mg of glucose in 100 ml of distilled water). b) Working standard: Dilute 10ml of stock standard solution in 100ml with distilled water in a volumetric flask.

Procedure

To take 0.2 to 1ml of working standard solution from five different test tubes and add water to bring the volume to 1ml in each test tube, add 4ml of anthrone reagent and mix the contents as well, then cover the test tube with a bath for 10 min, then cool the test tube to room temperature and measure the optical density in a photoelectric colorimeter at 620 nm (or) by using a red filter.

Simultaneously, prepare a blank with 1 ml of distilled water and 4 ml of anthrone reagent. Construct a calibration curve on graph paper by plotting the glucose concentration (10 to 100 mg) on the X-axis and the absorbance at 620 nm on the y-axis. 

Calculate the concentration of the sugar in the sample from the calibration curve. While calculating the sugar concentration in the unknown sample, the dilution factor has to be considered.

Report:

The amount of glucose present in the given sample is _______ mg/ml.

Frequently Asked Questions (FAQs)

  1. What is the importance of the Anthrone reagent?

    The Anthrone Reagent is a very important chemical in identifying drugs. This reagent allows a chemist to determine if a compound possesses features that indicate it is an amphetamine. It is used for tablet identification and to find out if any substances are controlled substances.

  2. What is the principle of the anthrone method?

    The anthrone test is a chemical test to find out the presence of indigo in natural dye formulations. Indigo is a blue-black dye often used to color jeans and other clothes. A common way to produce indigo is by fermentation of the plant Indigofera tinctoria. The anthrone test can also confirm if the dye in question was synthetic or natural, as artificial.

  3. What is the anthrone test used for?

    Anthrone is used to test the stability of dyes and to study the oxidative reactions of dyes.

  4. Which substance is estimated by the anthrone method?

    The anthrone method is a qualitative chemical test that identifies a substance as a carbohydrate and indicates the approximate proportion in which it is present. Traditionally, the anthrone method is used to measure the amount of zinc in an ore or metal.

  5. What does anthrone reagent do?

    Anthrone is a chemical that reacts with amino acids to produce a bright red color, and it is commonly used in the identification of proteins.

  6. What is carbohydrate estimation?

    Carbohydrates are the most important source of energy for the body. We all know that carbohydrates are the primary energy source in the diet. So there are two types of carbohydrate estimation: simple and complex. Simple carbohydrates are usually known as sugars, and they can drastically affect the body. Complex carbohydrates are rich in fiber, and they digest slowly and provide long-lasting and sustained energy. The main purpose of estimating carbohydrates is to ensure that the food choice is safe and within the specified carbohydrate intake of the patient.

  7. How to prepare anthrone reagent?

    The reaction should be carried out in a fume cupboard in a thoroughly dry atmosphere. Dryness is essential. The reagents are extremely sensitive to water, and I always carry out this procedure in a desiccator. A few small chips of Mg turnings are enough. You should make up the potassium permanganate solution fresh just before use. Anthrone (C8H6O) is best made up by adding 48 g. of the solid to a solution of 100 g. of concentrated sulfuric acid in 800 ml. of water. The solution should be cooled to 0 deg. C. with an ice bath and allowed to warm to room temperature over 1 or 2 hours in a stoppered flask. The reaction mixture should be distilled off, and the solid residue washed well with cold water and dried.

Few Other Protocols:

We hope you enjoyed our article about making a colorimetric determination of carbohydrates by usine Anthrone Method. With this knowledge, we know that you can make a colorimetric determination of carbohydrates using furfural, anthrone, and concentrated sulfuric acid. So what are you waiting for? Get to work!

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