ANNEX IIU.K.METHODS OF ANALYSIS TO VERIFY THE COMPOSITION OF CERTAIN SUGARS INTENDED FOR HUMAN CONSUMPTION
METHOD 7U.K. MEASUREMENT OF REDUCING SUGARS EXPRESSED AS INVERT SUGAR U.K.(Lane and Eynon constant volume modification)U.K.
6. Procedure U.K.
6.1. Standardization of Fehling's solution U.K.
6.1.1.Pipette 50 ml of solution B (4.1.2) and then 50 ml of solution A (4.1.1) into a clean dry beaker and mix well.U.K.
6.1.2.Rinse and fill the burette with 0·25 % (0·25 g/100 ml) standard invert sugar solution (4.3).U.K.
6.1.3.Pipette a 20 ml aliquot of the mixed solutions A and B (6.1.1) into a 500 ml boiling flask (5.1). Add 15 ml of water to the flask. Run in, from the burette, 39 ml of the invert sugar solution, add a small quantity of anti-bumping granules and mix the contents of the flask by gentle swirling.U.K.
6.1.4.Heat the flask and contents till boiling and allow to boil for exactly two minutes; the flask must not be removed from the heat source during the course of the rest of the procedure, or allowed to cease boiling.U.K.
Add three or four drops of methylene blue solution (4.4) at the end of the two-minute boiling period: the solution should be a definite blue colour.
6.1.5.Continue the standardization by adding, from the burette, the standard invert sugar solution in small increments, initially of 0·2 ml; then 0·1 ml and finally in single drops until the end-point is reached. This is indicated by the disappearance of the blue colour imparted by the methylene blue. The solution has then assumed the reddish colour associated with a suspension of copper I oxide.U.K.
6.1.6.The end-point should be reached at the end of three minutes from when the solution started to boil. The final titre, Vo, shall be between 39·0 and 41·0 ml. If Vo lies outside these limits, adjust the copper concentration of Fehling's solution A (4.1.1) and repeat the standardization process.U.K.
6.2. Preparation of sample solutions U.K.
The concentration of the sample test solution should be such that it contains between 250 and 400 mg invert sugar per 100 ml.
6.3. Preliminary test U.K.
6.3.1.A preliminary test must be carried out to ensure that the quantity of water to be added to the 20 ml of mixed solutions A and B is sufficient to ensure that a final volume after titration of 75 ml is obtained.U.K.
The same procedure as described in 6.1.4 is carried out except that the sample solution is used instead of the standard invert sugar solution, i.e. 25 ml of the sample solution is run into the flask from the burette. 15 ml of water is added, and the solution is allowed to boil for two minutes and then titrated until the end-point is reached as described in 6.1.5.
6.3.2.If, after the addition of the methylene blue solution, the reddish colour persists, the sample solution used is too concentrated. In this case, the test is discarded but repeated using a less concentrated sample solution.U.K.
If more than 50 ml of sample solution are required to obtain the reddish colour, a more concentrated solution of the sample must be used.
Calculate the quantity of water to be added by subtracting the volumes of mixed Fehling's solution (20 ml) and of the sample solution from 75 ml.
6.4. Final analysis of sample solution U.K.
6.4.1.Pipette into the boiling flask 20 ml of mixed Fehling's solution and the quantity of water determined as in 6.3.U.K.
6.4.2.Add, from the burette, the observed titre of the sample solution (as determined in 63) less 1 ml. Add some anti-bumping granules, mix the contents of the flask by swirling, boil the flask and contents and titrate as previously (6.3). The end-point should be reached one minute from the time of addition of the methylene blue solution. Final titre = V1.U.K.