ASTM D1364 for Water in Volatile Solvents (Karl Fischer Reagent Titration Method)
10. Procedure
10.1 Introduce 10 to 25 mL of the anhydrous solvent mixture (pyridine-glycol, 1 + 4) into the titration vessel, making sure, if an instrument end point apparatus is used, that the electrodes are covered by this amount of solvent. If the color end point is to be determined, make up a second flask as well.
10.2 Adjust the stirrer, if any, to provide adequate mixing without splashing. Titrate the mixture to the instrumental end point (see 3.1), or the color end point (see 3.1.2 ), with Karl Fischer reagent. If the color end point is to be observed, titrate one flask to the orange-red end point and the second to match the first. Set aside the first flask as a comparison standard for titrating the specimen.
10.3 To the titration mixture thus prepared, add an amount of specimen as indicated in Table 1. Exercise care when the specimen is transferred so that water is not absorbed from the air, particularly under conditions of high humidity. Again, titrate the mixture with Karl Fischer reagent to the same instrumental or color end point previously employed. Record the amount of reagent used to titrate the water in the specimen.
NOTE 5 - (a) Ketones - In titrating ketones when greatest precision is required, cool the reaction mixture in ice water during the addition of Karl Fischer reagent.
(b) Organic Acids - Cool the reaction mixture in ice water prior to the addition of Karl Fischer reagent.
NOTE 6 - When using the volumetric flask type titration vessel in humid climates, place a piece of thin sheet rubber over the mouth of the vessel; provide a small hole for introducing the buret tip. In less humid climates it is sufficient to lower the tip of the buret deeply into the long neck of the titration flask.
NOTE 7 - In titrating with the volumetric flask type titration vessel, avoid wetting the stopper and upper end of the flask with either the reagent or the sample solvent. Each time the titration is interrupted, touch the buret tip to the neck of the flask to remove droplets which, if not removed, would absorb moisture from the atmosphere. When the flask is removed from under the buret tip, wipe the tip with a clean dry cloth in a downward motion.
11. Calculation
11.1 Calculate the water content of the specimen as follows:
Water, %, by weight = (V x W)/(10 x S)
where:
V = volume of Karl Fischer reagent required for titrating by the specimen, mL,
W = equivalency factor for Karl Fischer reagent, water per millilitre of reagent, mg, and
S = specimen weight used, g.
NOTE 8 - If specimen was added volumetrically by means of a calibrated volumetric pipet, then S = volume of specimen x density of specimen, g.
