MIL-PRF-23942A(AS)
e. Buret, 10 mL.
f. Platinum electrodes, furnished with a commercial titrimeter.
g. Hypodermic syringe. The metal end of a 5-mL hypodermic syringe is removed and the
glass opening is enlarged to 3 mm. This syringe is used for transferring weighed samples of the
polymer.
4.5.8.2 Reagents and materials.
a. Karl Fischer reagent, or equivalent, available from Mallinckrodt or Fischer Scientific Co.
b. Karl Fischer reagent diluted 50 volume percent with Karl Fischer grade methanol.
c. Titration solvent consisting of a mixture of 10 mL methanol, 20 mL pyridine, 10 mL of
glacial acetic acid and 160 mL of chloroform. All solvents shall be ACS reagent grade except
Karl Fischer grade methanol.
4.5.8.3 Standardization of reagent. Place 200 mL of dry methanol in the titration flask and
titrate with Karl Fischer reagent to the end point. Add 0.06 g of water from a weighing pipet or
a weighed amount of sodium tartrate equivalent to 0.06 g of water. Titrate again to the end point
and record the volume of Karl Fischer reagent used. Repeat by adding successive weighed
amounts of water or sodium tartrate and titrating until satisfactory checks are obtained. Duplicate
titer values shall be within 0.00002 g water per mL of Karl Fischer reagent.
grams water
Titer =
mL Karl Fischer reagent
4.5.8.4 Procedure. Add 200 mL of the titration solvent to the titration flask and titrate to a
dead-stop end point with the Fischer's reagent. Slightly before the end point is reached
(detectable by a change of color of the titration mixture), adjust the electric eye so that it is barely
closed. At the end point, the electric eye should remain open for at least 60 seconds with one
drop of reagent. If extremely dry titration solvents are used, the electric eye may not be able to be
adjusted. This can be corrected by adding a drop of water and then titrating with the Karl Fischer
reagent, or equivalent, to the end point (see 6.4.5). After the end point is reached, add a
weighed 5-g sample from the modified hypodermic syringe. Titrate slowly near the end point
with the Karl Fischer reagent to the same 60 second end point used in pretitrating the titration
solvent. Calculate percent water as follows:
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