ASTM D1364 for Water in Volatile Solvents (Karl Fischer Reagent Titration Method)
4. Summary of Test Method
4.1 This test method is based essentially upon the reduction of iodine by sulfur dioxide in the presence of water. This reaction can be used quantitatively only when pyridine and an alcohol are present to react with the sulfur trioxide and hydriodic acid produced according to the following reactions:
H2O + I2 + SO2 + 3C5H5N →2C5H5N•HI + C5H5N•SO3
C5H5N•SO3 + ROH →C5H5N•HSO4R
4.2 To determine water, Karl Fischer reagent (a solution of iodine, pyridine, and sulfur dioxide, in the molar ratio of 1 + 10 + 3) dissolved in anhydrous 2-methoxyethanol is added to a solution of the sample in anhydrous pyridine-ethylene glycol (1 + 4) until all water present has been consumed. This is evidenced by the persistence of the orange-red end-point color; or alternatively by an indication on a galvanometer or similar current-indicating device which records the depolarization of a pair of noble-metal electrodes. The reagent is standardized by titration of water.
5. Significance and Use
5.1 Volatile solvents are used in a variety of chemical processes which may be affected by water. Therefore, this test method provides a test procedure for assessing compliance with a specification.
