4/9/98
A-36 Application of the Hygrometer (900-901D1)
B. Instructions for Preparing Known Samples
Note: This procedure is only for liquids that are highly miscible
with water. Excessive equilibrium times would be
required with less miscible liquids.
To prepare samples of known moisture content, use the apparatus
in Figure A-3 and complete the following steps:
1. Weigh the dry, empty apparatus.
2. Fill the glass bottle with the sample liquid.
3. Open both valves and turn on the magnetic stirrer.
4. While monitoring the dew point reading with the hygrometer,
bubble dry N
2
through the liquid until the dew point stabilizes
at some minimum value.
5. Turn off the N
2
supply and close both valves.
6. Weigh the apparatus, including the liquid, and calculate the
sample weight by subtracting the step 1 weight from this
weight.
7. Insert a syringe through the rubber septum and add a known
weight of H
2
O to the sample. Continue stirring until the water
is completely dissolved in the liquid.
8. Record the dew point indicated by the hygrometer and
calculate the moisture content as follows:
9. Repeat steps 6-8 until samples with several different moisture
contents have been analyzed.
Note: The accuracy of this technique can be checked at any
point by withdrawing a sample and performing a Karl
Fischer titration. Be aware that this will change the total
liquid weight in calculating the next point.
PPM
W
weight of water
total weight of liquid
--------------------------------------------------
10
6
×=
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