exp 1 - Title : Determination of glucose by the...

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Title : Determination of glucose by the Nelson-Somogyi’s method Objectives : 1. To determine glucose concentration by using the Nelson-Somogyi’s method. 2. To learn how to calibrate the spectrophotometer for biological and chemical studies purpose. 3. To constructs a standard curve of glucose concentration by measuring absorbance. 4. To determine the glucose concentration of the milk sample extract. Principle : By using the Nelson-Somogyi’s method, the concentration of glucose and other reducing sugars can be determined. This can be done when the sample extract or test solution is heated together with alkaline tartrate. This will result the reducing of copper from the cupric to cuprous state. Hence, this causes cuprous oxide to be formed. When cuprous oxide is react with arsenomolyybdate reagent, it will formed molybdenum blue which causes the appearance of violet coloured complex. The colour develop is compared with a set of standards in a colorimeter at 500nm. Introduction : Monosaccharide is a monomer of carbohydrate. In monosaccharide, all of the carbon atoms except one have a hydroxyl group attached. Monosaccharides can either aldose or ketose based on the position of carbonyl group. Sugar that have aldehyde group is called aldose or aldo sugar while sugar with keto group is called ketose or keto sugar. Glucose is a hexose sugar and from the aldose group and has a formula of C 6 H 12 O 6 . Reducing sugars are sugar that contain aldehyde or ketone group. Therefore, all monosaccharides are reducing sugars. When reducing sugars react with other substances, it will go through the process of oxidation-reduction chemistry. Oxidation is the process where
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electrons being removed while reduction is the process of gaining electrons. From the reaction, it produced a reduced substance plus the oxidized sugar molecule. Hence, reducing sugar that have an aldoses group acts as reducing agent where it can give up the electrons. The oxidising agent is reduced by receiving the electrons. Carboxylic acid group will produce from the oxidation of the aldehyde group. Ketoses act as weak reducing sugars under alkaline conditions this is due to that they will partially isomerize to aldoses. Nelson-Somogyi’s method is one of the classical and widely used for determined the amount of reducing sugars. The Cu 2+ ions that been used in this experiment is being reduced to Cu + ions by reducing sugar. The arsenomolybdate complex which is prepared by reacting ammonium molybdate , (NH 4 ) 6 Mo 7 O 24 and sodium arsenate, Na 2 HAsO 7 in sulphuric acid is then being reduced by Cu + ions. An intense, stable blue colour is produced from the reduction of the arsenomolybdate complex. The colour develop is measured spectrophotometrically with the absorbance value at 500nm. A standard curve of glucose concentration with its absorbance value needs to be constructed because the reaction is not stoichiometric. The Nelson-Somogyi’s method need to be conducted under the proper conditions to
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This note was uploaded on 07/10/2011 for the course CHEM 1214 taught by Professor Dr.tey during the Spring '11 term at University of Tunku Abdul Rahman.

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exp 1 - Title : Determination of glucose by the...

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