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

METHOD 6

DETERMINATION OF pH

1. SCOPE AND FIELD OF APPLICATION

This method determines the pH of:

• caseinates.

2. DEFINITION

The pH of caseinates: the pH, at 20 ^oC, of an aqueous solution of caseinates, as determined by the method specified.

3. PRINCIPLE

The electrometric determination of pH of an aqueous solution of caseinate, using a pH meter.

4. REAGENTS

Any water used in the preparation of the reagents or in the Procedure (6) shall be recently distilled water that has been protected from carbon dioxide absorption.

4.1. Buffer solutions, for calibration of the pH meter (5.2)

Two standard buffer solutions with pH values at 20 ^oC which are known to the second decimal place and will bracket the pH value of the sample under test, for example phtalate buffer solution of pH approximately 4 and a borax buffer solution of pH approximately 9.

5. APPARATUS

5.1. Balance, accuracy 0,1 grams.

5.2. pH meter, minimum sensitivity 0,05 pH unit, with a suitably calibrated elecrode, e.g. glass electrode and a calomel or other reference electrode.

5.3. Thermometer, accuracy 0,5 ^oC.

5.4. Conical flask, capacity 100 ml, fitted with a ground glass stopper.

5.5. Beaker, capacity 50 ml.

5.6. Mixer

5.7. Beaker, for the mixer (5.6) of at least 250 ml capacity.

6. PROCEDURE

6.1. Preparation of the test sample

As described in Section 1.2 of the General Provisions.

6.2. Determination

6.2.1. Calibration of pH meter

Adjust the temperature of the buffer solutions (4.1) to 20 ^oC and calibrate the pH meter in accordance with the manufacturer's instructions.

NOTES

1. The calibration should be carried out while the flasks are standing for 20 mintues (see 6.2.2).

2. If a series of samples is being tested, check the calibration of the pH meter with one or more of the standard buffer solutions at least every 30 minutes.

6.2.2. Preparation of the test solution

Transfer to the beaker (5.7) 95 ml of water, add 5,0 grams of the test sample (6.1), and mix using the mixer (5.6) for 30 seconds.

Allow to stand for 20 minutes at about 20 ^oC, covered with a watch glass.

6.2.3. Measurement of pH

6.2.3.1. Pour about 20 ml of the solution into the beaker (5.5) and immediately determine the pH of this liquid, using the pH meter (5.2) after having rinsed the glass electrode carefully with water.

6.2.3.2. Measure the pH.

7. EXPRESSION OF RESULTS

7.1. Recording of pH

Record, as the pH of the aqueous solution of caseinate, the value read from the dial of the pH meter to at least two decimal places.

7.2. Repeatability

The difference between the results of two determinations carried out simultaneously or in rapid succession on the same sample, by the same analyst, under the same conditions, shall not exceed 0,05 pH unit.

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