Proportioning of glucose by the DNS

The proportioning of glucose by the DNS is a colorimetric Dosage Glucose.

Principle

One uses the reducing properties of the Glucose. Hot and in Alkaline medium, there is 3,5-dinitrosalycilic reduction of the acid: DNS (acid 2-hydroxy-3,5-dinitrobenzoïque) which plays the part of oxidant, glucose being the reducer.

Reaction of 3,5-dinitrosalicylic reduction of the acid in 3-amino-2-hydroxy-5-nitrobenzoïque acid (3-amino-5-nitrosalicylic):

glucose, as for him is oxidized in various products of oxidation:

Glc \ longrightarrow produced \, of oxidation + ne^ {-}

The acid 3-amino-5-nitrosalicylic is a red compound. This reaction is not stoechiometric: there is no assessment of oxydoreduction. The intensity of red coloring is proportional to the concentration of the Ose if one operates under constant physicochemical conditions. The calibration lines always do not pass by the origin.

This method is not applicable to the proportioning of a complex mixture of reducing glucids.

Protocol

material

Spectrophotometer;
washed and dry tubes tests;
automatic Pipette;
Beaker S;
tanks with spectrophotometer.

Solutions

DNS;
Solution of glucose with 0.0100 mol/L;
distilled water;
Solution to be proportioned.

Stages

Preparation of the range of calibration

In a series of tubes:

to introduce 0-0,3-0,6-0,9-1,2-1,5 ml of solution of glucose with 0.0100 mol/L
To adjust each tube to 3 ml with water distilled
To add 2mL of reagent 3-5 DNS

To mix and stop the tubes with carded cotton and aluminum foil. To carry to the Bath Marie to 100°C during 5 minutes exactly. To cool and add 15 ml of water distilled in each tube, to homogenize and let rest during 15 minutes. Liras absorptances with 350 Nm against the witness.

Tests

They are to be treated under the same operating conditions.
To carry out proportioning with test specimens of 0,5 and 1 ml

Colorimetric table

This table represents what must be put in each tube and in which quantity.

Attention: for water, one does not make distinction between the water which is put before and after the Marie bath. precisely if! too much water before the DNS changes the pH and modifies the reaction….the purpose of water after is to dilute so that the absorptance enters the limits of the spectro!

measure with 540 Nm and not to 350

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