ISO 12937 Petroleum products - Determination of water - Coulometric Karl Fischer titration method
WARNING - The use of this International Standard may involve hazardous materials, operations and equipment. This International Standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this International Standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1 Scope
This International Standard specifies a method for the direct determination of water in petroleum products boiling below 390 °C. It covers the mass fraction range 0.003 % (m/m) to 0.100 % (m/m). It is not applicable to products containing ketones or to residual fuel oils.
This International Standard may be applicable to lubricating base oils. However, the precision has not been established for these materials.
The precision given in clause 12 is based upon data obtained using dual-cell, dual-electrolyte systems.
NOTE 1 A number of substances and classes of compounds associated with condensation or oxidation-reduction reactions interfere in the determination of water by Karl Fischer titration. In petroleum products, the most common interferences are hydrogen sulfide and mercaptan sulfur, however, mass fractions of these below 0.003 % (m/m) as sulfur will not cause significant interference over the range 0.003 % (m/m) to 0.100 % (m/m) water. Other organic sulfur compounds commonly present such as sulfides, disulphides and thiophenes, do not interfere.
NOTE 2 An alternative procedure is provided for information in annex B for the direct determination of water over the range 0.003 % (V/V) to 0.100 % (V/V) in petroleum products. The limitations under which this alternative volume measurement may be used are listed in annex B.
NOTE 3 For the purposes of this International Standard, the terms "% (m/m)" and "% (V/V)" are used to represent the mass and volume fraction of a material respectively.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards.
ISO 3170:1988, Petroleum liquids - Manual sampling.
ISO 3171:1988, Petroleum liquids - Automatic pipeline sampling.
ISO 3696:1987, Waterforanalyticallaboratoryuse - Specification andtest methods.
3 Principle
A sample is visually inspected (see 6.2.1). If clear and bright, and free from both water droplets and particulate matter on swirling, a weighed portion is injected into the titration vessel of a coulometric Karl Fischer apparatus in which iodine for the Karl Fischer reaction is generated coulometrically at the anode. When all the water has been titrated, excess iodine is detected by an electrometric end-point detector and the titration is terminated. Based on the stoichiometry of the reaction, one mole of iodine reacts with one mole of water, thus the quantity of water is proportional to the total integrated current according to Faraday's Law.
If the sample is not clear and bright, or water droplets or particulate matter are observed on swirling, a portion of a solution of sodium dioctylsulfosuccinate is added prior to homogenizing with a mixer. A weighed portion is then treated as described above.
