First Commission Directive of 25 October 1985 on methods of analysis for edible caseins and caseinates (85/503/EEC)

METHOD 4

DETERMINATION OF ASH (including P₂O₅)

1. SCOPE AND FIELD OF APPLICATION

The method determines the ash (including P₂O₅) content of:

• acid caseins

2. DEFINITION

The ash (including P₂O₅) content: the content of ash as determined by the method specified.

3. PRINCIPLE

A portion of the sample is incinerated at 825 ^o C ± 25 ^o C in the presence of magnesium acetate to bind all phosphorus of organic origin. The final ash is calculated after the weighing of the residue and subtraction of the mass of ash originating from the magnesium acetate.

4. REAGENTS

4.1. Magnesium acetate tetrahydrate solution, 120 g/1. Dissolve 120 grams of magnesium acetate tetrahydrate [Mg (CH₃ CO₂)₂ 4 H₂ O] in water and make up one litre with water.

5. APPARATUS

5.1. Analytical balance

5.2. One-mark pipette, 5 ml.

5.3. Silica or platinum dishes, about 70 mm diameter and 25 to 50 mm deep.

5.4. Drying oven, capable of being controlled at 102 ^oC ± 1 ^oC.

5.5. Electrical furnace, capable of being controlled at 825 ^oC ± 25 ^oC.

5.6. Boiling water bath

5.7. Desiccator containing freshly activated silica gel with a water content indicator or an equivalent desiccant.

6. PROCEDURE

6.1. Preparation of the test sample

As described in Section 1.2 of the General Provisions.

6.2. Preparation of the dishes

Heat two dishes (A,B) (5.3) in the electrical furnace (5.5), controlled at 825 ^o C ± 25 ^o C, for 30 minutes. Allow the dishes to cool somewhat and then place in the desiccator (5.7) to the temperature of the balance room and weigh to the nearest 0,1 mg.

6.3. Test portion

Weigh, to the nearest 0,1 mg approximately 3 grams of the test sample (6.1), directly into one of the prepared dishes (A).

6.4. Determination

Using the pipette (5.2), add to the dish (A) exactly 5 ml of the magnesium acetate solution (4.1) so as to wet all of the test portion, and allow to stand for 20 minutes.

To the other prepared dish (B), add with the pipette (5.2) exactly 5 ml of the magnesium acetate solution (4.1).

Evaporate the contents of both dishes (A and B) to dryness on the boiling water bath (5.6).

Place both dishes in the oven (5.4), controlled at 102 ^oC ± 1 ^oC, for 30 minutes.

Heat dish A with its contents on a low flame, a hot plate or under an I/R lamp, until the test portion is completely charred, taking care that it does not burst into flame.

Transfer both dishes (A and B) to the electrical furnace (5.5), controlled at 825 ^oC ± 25 ^oC, and heat for at least one hour until all carbon has disappeared from dish A. Allow both dishes to cool somewhat and then place in the desiccator (5.7) to the temperature of the balance room and weigh to the nearest 0,1 mg.

Repeat the operations of heating for approximately 30 minutes, in the electrical furnace (5.5), cooling and weighing, until the mass remains constant to within 1 mg or begins to increase. Record the minimum mass.

7. EXPRESSION OF RESULTS

7.1. Method of calculation

The content of ash, including P₂O₅, in the sample, as a percentage by mass, is given by:

where:

m₀

is the mass, in grams, of the test portion;

m₁

is the mass, in grams, of dish A and residue;

m₂

is the mass, in grams, of the prepared dish A;

m₃

is the mass, in grams, of dish B and residue;

m₄

is the mass, in grams, of the prepared dish B.

Calculate the final result to the nearest 0,01 %.

7.2. Repeatability

The difference in results between the determinations carried out simultaneously or in rapid succession on the same sample, by the same analyst, under the same conditions, shall not exceed 0,1 grams per 100 grams of product.

The repeatability interval should be achieved in 95 % of the times that the method is correctly carried out.