ISO 4316:1977 pdf dwonload – Surface active agents – Determination of pH of aqueous solutions – Potentiometric method
1 SCOPE AND FIELD OF APPLICATION
This International Standard specifies a method for the determination of the pH of aqueous solutions of surface active agents.
This method is applicable only if so indicated in the specific standard for each product.
2 REFERENCE
IS0 607, Surface active agents – Detergents – Methods of sample division. 1 )
3 PRINCIPLE
Potentiometric measurement of the potential difference between a glass electrode and a reference electrode dipping in an aqueous solution of the surface active agent.
4 REAGENTS
4.1 Distilled water, free from carbon dioxide and protected from its absorption.
4.2 Standard buffer solutions.
Two standard buffer solutions, chosen from those common- ly used, are necessary to calibrate the pH meter. Their pH values should, if possible, be on either side of the expected pH of the test solution but, if not, one should not differ from the expected pH by more than 1 pH unit.
5 APPARATUS
5.1 pH meter, including a temperature compensation system, and graduated in 0,l pH unit.
5.2 Glass electrode.
5.3 Electrode, calomel/saturated potassium chloride type.
5.4 Combined electrode, as an alternative to the glass electrode (5.2) and reference electrode (5.3).
6 SAMPLING
The laboratory sample of the surface active agent shall be prepared and stored according to the instructions given in ISO 607.
7 PROCEDURE
7.1 Test portion
Weigh, to the nearest 0,Ol g, approximately 10 g of the laboratory sample.
7.2 Determination
7.2.1 Preparation of the test solution
The preparation and the concentration of the test solution from the test portion (7.1) shall be indicated in the specific standard for each product.
7.2.2 Calibration
Calibrate the pH meter (5.1) according to the manufac-turer’s instructions, using the two standard buffer solutions (4.2) chosen, at the temperature specified in 7.2.3.
7.2.3 pH measurement
For all measurements, the temperatures of the electrodes,of the water used for washing and of the standard buffer solutions or the test solutions, shall be adjusted to 20 + 1 ‘C and should be as close to each other as possible.
These temperatures shall not differ by more than 1 “C.
Once the apparatus has been calibrated, wash the electrodes first with the water (4.1) and then with the test solution (7.2.1). Mix the test solution (7.2.1), place a sufficient volume in the measuring vessel and dip the electrodes in it. Check that the reading of the pH meter is stable for 1 min, and then record the value. Repeat the same operations with a fresh portion of the test solution. If the second measurement differs from the first by 0,l pH unit (or more), carry out a third measurement. If this value is inconclusive, repeat the test, including the calibration. NOTE – In the case of cationic surface active agents, re-calibrate the pH meter after every measurement.