ISO 12937 Petroleum products - Determination of water - Coulometric Karl Fischer titration method
4 Chemicals and materials
4.1 Molecular sieve pellets, type 4A.
Activate in an oven at 200 °C to 250 °C for 4 h. Transfer immediately to a dry sealable bottle or desiccator and allow to cool.

4.2 Xylene, reagent grade.
Dry by adding approximately 100 g of activated molecular sieve (4.1) to 2 litres of xylene. Allow to stand overnight.

4.3 Karl Fischer reagents
Use commercially available reagents that meet the performance requirements described in clause 8.
4.3.1 Anode electrolyte solution (anolyte)
Mix 6 parts by volume of commercial Karl Fischer anode solution with 4 parts by volume of dry xylene (4.2).

NOTE Other proportions of Karl Fischer anode solution and xylene may be used, provided they meet the performance criteria of clause 8.

4.3.2 Cathode electrolyte solution (catholyte)
Use commercially available Karl Fischer cathode solution.

4.3.3 Single Karl Fischer solution, for use in place of dual electrolyte solutions (4.3.1 and 4.3.2) in cells with or without a diaphragm.

4.4 Sodium dioctylsulfosuccinate, reagent grade.
NOTE 1 Sodium dioctylsulfosuccinate is also sold under the names dioctyl ester of sodium sulfosuccinic acid and dioctyl sulfosuccinate sodium salt.

NOTE 2 Other anionic surfactants may be used in place of sodium dioctylsulfosuccinate, provided they meet the requirements of normative annex A.

4.4.1 Sodium dioctylsulfosuccinate solution
Dry sodium dioctylsulfosuccinate (4.4) in an oven at 105 °C to 110 °C for 4 h. Transfer immediately to a dry sealable bottle or desiccator and allow to cool. Once cool, dissolve 10 g of dried sodium dioctylsulfosuccinate in dry xylene (4.2) and make up to 100 ml with dry xylene. The mass fraction of water in this solution shall be less than 0.010 % (m/m) when checked by the procedure given in clause 9.

4.5 Water, conforming to grade 3 of ISO 3696.

5 Apparatus
5.1 Automatic coulometric Karl Fischer titrator, capable of meeting the requirements given in clause 8.

5.2 Non-aerating mixer, capable of meeting the homogenization requirements given in A.3.

NOTE Both insertion mixers and circulating mixers, such as those used with automatic sampling containers, are acceptable provided they comply with the principles of annex A.

5.3 Syringes, of glass, with needles of suitable length such that the tip can reach under the surface of the anolyte when inserted through the inlet-port septum. The bores of the needles used shall be kept as small as possible, but large enough to avoid problems arising from back pressure or blocking whilst sampling.

NOTE 1 Needles with bores between 0.5 mm and 0.8 mm have been found suitable.

NOTE 2 Recommended syringe sizes are

a) 10 μl with a fixed needle for periodic checking of the titrator performance,
b) 1 ml or 2 ml for petroleum product samples, and
c) 10 ml for addition of the sodium dioctylsulfosuccinate solution to petroleum product samples which are not clear and bright, or which contain free water or particulate matter.

5.4 Balance, capable of weighing to +/- 0.1 mg.

5.5 Volumetric flask, capacity of 100 ml.

5.6 Sealable bottles or desiccators, to hold activated molecular sieve and dried sodium dioctylsulfosuccinate.

5.7 Ovens, capable of maintaining temperatures of 105 °C to 110 °C and 200 °C to 250 °C.

5.8 Cooling bath, if required, capable of meeting the requirements of 6.2.8.

5.9 Thermometer, capable of measuring the sample temperature to the nearest 1 °C.