WATER IN SOLVENTS BY KARL FISCHER TITRATION: D1364
EXPLANATION
This test method covers the determination of water in any proportion in volatile solvents and chemical intermediates used in paint, varnish, lacquer, and related products. This test method is not applicable in the presence of mercaptans, peroxides, or appreciable quantities of aldehydes or amines.
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 + C5H5•SO3
C5H5N•SO3 + ROH → C5H5N•HSO4R
TEST SUMMARY
To determine water, 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.
TEST PRECISION
Repeatability: 0.015 % absolute
Reproducibility: 0.027 % absolute
