ISO 4317:2011 pdf free download – Surface-active agents and detergents – Determination of water content一 Karl Fischer methods.
5.3.3.3 Injector, with a capacity of 1 ml to 20 ml, the outside diameter of the needle measuring 1 mm to
2 mm and the length of the needle 50 mm to 100 mm. A rubber plug shall be fixed at the end of the needle for sealing: a round-type silicone rubber, 13 mm to 15 mm in diameter and 5 mm to 7 mm in thickness, may be used for this purpose.
5.3.3.4 Balance, accurate to 0,1 mg. An electrobalance may conveniently be used if it is connected to an automatic titration device through a suitable interface.
5.3.4 Sampling
The laboratory sample of surface active agent or detergent shall have been prepared and stored in
accordance with the instructions given in ISO 607.
5.3.5 Procedure
5.3.5.1 Calibration of titration device
Make the inside of an electrolytic cell anhydrous by coulometric titration until an end point is reached while stirring anolyte in the electrolytic cell. Inject 5 p1 of water into the anolyte using a microsyringe and carry out coulometric titration until an end point is reached in order to find water content. Repeat this procedure two times or more, and confirm that the water content found by this procedure falls within the range of 5 000 pg ± 250 pg. If it is out of this range, after renewing the electrolytic solution or washing an electrode or diaphragm, carry out a calibration.
5.3.5.2 Determination of water content
Place about 100 ml of anolyte into the anode room of an electrolytic cell and about 5 ml of catholyte in the cathode room. Closely seal the electrolytic cell and mount it on the titration apparatus after it has been set up.
While stirring ariolyte in the electrolytic cell. coulometrically titrate it to get an end point, and make the inside anhydrous. The volume of titrant in this case does not need to be read.
The existence of free iodine in the anolyte prevents the electrolytic current from flowing, so it is preferable to add water, water-alcohol solution or water-propylene carbonate solution to obtain an excess of water of 2 000 pg to 3 000 pg.
Wash the injector (5.3.3.3) before use, dry it and keep it in a desiccator.
Take the injector out of the desiccator and attach a rubber plug to the end of the injector needle.
Remove the plug, stick the injector needle as deeply as possible into the sample (which preferably contains
0,5 mg to 5 mg of water) in the sample container, gently draw the plunger, and take the sample up by about
1110 of the volume of the injector.
Take the injector out of the sample container, invert the injector so that the needle is pointing upwards to remove air, attach a rubber plug to the tip of the needle, slightly apply pressure in order to let the sample moisten the ground surfaces, then discharge the sample.
Carry out this operation (washing the injector with the sample) two or three times.
Gradually take the sample over to the scale of the injector, discharge excessive sample to adjust it to the scale while orienting the injector upward, and simultaneously expel the air kept inside. Immediately attach the rubber plug to the tip of the needle. Weigh the mass of the injector with sample to the nearest 0,1 mg.
6.1.2 Reproducibility
The absolute difference between two independent single test results, obtained using the same method on identical test material in different laboratories by different operators using different equipment, will not exceed the reproducibility limit, R, in more than 5 % of cases.
According to the ring test results given in Annex B, the reproducibility limit, R, shall be
less than or equal to 0,026 gIl 00 g for a water content of approximately 0,24 % (mass fraction), or less than or equal to 3,79 gIl 00 g for a water content of approximately 28,8 % (mass fraction).
6.2 Precision of the coulometric titration method
6.2.1 Repeatability
The absolute difference between two independent single test results, obtained using the same method on identical test material in the same laboratory by the same operator using the same equipment within a short interval of time, will not exceed the repeatability limit, r, in more than 5 % of cases.
According to the ring test results given in Annex B, the repeatability limit, r, shall be
— less than or equal to 0,007 gIl 00 g for a water content of approximately 0,04 % (mass fraction), or
— less than or equal to 0,016 gIl 00 g for a water content of approximately 0,23 % (mass fraction).